The apocalypse has become big business. And it's getting bigger every day.

In the ’50s, homeowners fearing Communist attacks built bunkers in their backyards and basements, hung up a few “God Bless Our Bomb Shelter” signs and called it a Cold War.

But today, Americans en masse are again preparing for the worst—and Communists are just about the only thing not on their list. What is? Terrorist attacks, a total economic collapse, perhaps even zombie invasions. Or maybe just a complete societal breakdown after this November's scorched-Earth presidential election.

But this is not your Uncle Travis' guns-and-canned-foods-militia vision of Armageddon preparedness. While the fears of survivalists and so-called preppers are modernizing, so too are their ideas and methods of refuge.

The business of disaster readiness is getting higher-tech, higher-priced, and way more geographically diverse, with state-of-the-art underground shelters tricked out with greenhouses, gyms, and decontamination units in the boondocks and the latest in plush panic rooms in city penthouses.

Welcome to the brave (and for some, highly profitable) new world of paranoia.

“There's a lot of uneasiness in society. You see it in politics. You see it in the economy. The world is changing really, really quickly and not always for the better,” says Richard Duarte, author of “Surviving Doomsday: A Guide for Surviving an Urban Disaster.”

Prepping “gives them a certain comfort that at least they’ve got some sort of preparations to ... take care of their family if things start falling apart all around them,” he says.

Better be safe with a safe room

If the booming sales of panic rooms are any indication, more and more city dwellers these days are obsessively worrying about everything from home invasions to terror attacks. And they're backing up those worries with cold, hard cash.

Sales of safe (aka panic) rooms, where families can safely lock themselves away from most threats, are up 30% over the same time last year at Gaffco Ballistics, a Londonderry, VT–based installer which does much of its business in New York City, according to CEO Tom Gaffney. That's driven in part by the terrorist attacks in San Bernardino, CA, and Paris, he says.

Most of his safe rooms are actually fortified master bedrooms, with ballistic fiberglass–reinforced walls, a Kevlar-lined door that is purported to resist both bullets and sledgehammers, and bullet-proof windows—as well as a high-end alarm system that is designed to withstand burglars, rioters, and more.

Panic room controls Gaffco Ballistics LLC

He also turns home theaters into radiation-proof rooms where residents can watch the latest Hollywood blockbusters while World War III rages on outside.

The rooms range from $250,000 to $1.5 million. (No one said paranoia came cheap.)

People are “just more aware” of potential threats, says Gaffney of his clients, many of whom don't consider themselves preppers. “It's a growth market.”

That paranoia has also been fueling business at construction company and safe room installer GoNavco Corp., a Troy, NY–based safe room installer.

Owner Joe Navarra began installing panic rooms several years ago after requests began pouring in. Now this burgeoning portion of his business is up about 50% over the same time last year.

His no-frills chambers start at $20,000, although most are in the $50,000 range. They're typically installed in the closets or bathrooms of master bedrooms.

Panic rooms aren't just relegated to the biggest cities and the biggest disasters. Author Duarte has several spaces in his suburban home outside of Miami that could serve as safe rooms with fortified walls and doors.

“You're never going to stop a determined attacker” with his homemade safe rooms, says Duarte, who says he became a prepper after Hurricane Andrew destroyed his home in 1992. “But you can slow them down to give you enough time to call the police or figure out how to defend yourself.”

Survivalist properties: Living off the land

Of course, for some survivalists, cities will never feel safe. These are the folks who need to go far off the grid. But even this age-old concept is getting a makeover, and a business plan.

Some real estate companies are seeing big increases by specializing in “survivalist properties”—large parcels of rural land with homes targeted specifically to preppers, with full fortification and self-sustainable food and energy options. After all, why not grow your own tomatoes and kale while you wait out the end of the world as we know it?

For example, sales at American Redoubt Realty, a real estate firm nestled in the heart of prepper country in northern Idaho, are up 50% over the same time last year, says real estate agent Todd Savage, who specializes in such transactions. His clients typically hail from Texas and California.

Idaho, Montana and Wyoming are often considered the epicenter of the modern survivalist property trend. But you can find pockets of it across the country, from North Carolina to Washington state.

“Each election cycle we see a huge uptick in interest and sales,” says Savage, who first noticed the trend in 2012, when Mitt Romney faced off against Barack Obama. “People are tired of both sides.”

His buyers are looking for very specific, “100% self-sustainable,” rural properties, at least 10 acres and up, says Savage. To make it true prepper property, the land must have at least two abundant water sources, like a well and a stream; alternative energy, like solar panels or hydropower; and the ability to grow food.

It must also be easily defendable against a multitude of threats, with either bunkers or safe rooms or simply reinforced doors and windows and a lot of ammunition.

Properties already outfitted with solar panels or hydropower are particularly in demand since they can be expensive to install, he says.

Self-sustaining power sources such as solar are key. AmericanRedoubtRealty.com

Survivalists are also particularly hungry for metal containers they can convert into shelters and bury underground, as well as Quonsets, those steel, half-moon-shaped shelters that can be built into mountainsides, says Jake Crites, a real estate broker at Jake’s Old West Properties in Ashfork, AZ. He's seen a big uptick over the past two years.

Emergency Quonset jakesoldwestproperties.com

Better have deep pockets for a bunker

Likewise, sales at bunker builder Rising S Co. have never been better. They shot up 20% to 25% over the past two years for the radiation-resistant shelters, which can be sunk 33 feet underground and tricked out with gyms, greenhouses, and water filtration systems that can even enable dwellers to drink their own urine if need be. Ewww!

“The more politics that are played on TV, the more our sales go up,” says proud prepper Clyde Scott, owner of the Kemp, TX–based company. “People are in fear of our government passing laws to take their guns away and not allowing them to protect themselves,” including against a foreign invasion.

The company sells nearly two dozen, air- and water-tight steel bunkers a year, which can range from $40,000 to $10 million each. They bear little resemblance to the bare-bulb bomb shelters of the '50s. The bulk of sales are in Texas, but the end-of-the-world-proof shelters are also big in the Carolinas, Virginia, and Florida, Scott says.

Bunkers soon to be under 10 feet of dirt ultimatebunker.com

Most of his clients, from surgeons to billionaires, work in cities and are successful businesspeople with families. The bunkers are typically installed on their “bug out” properties, secondary residences in the country where preppers can go if (or when, depending on whom you talk to) disaster hits.

Business is also good over at Ultimate Bunker, based on the outskirts of Salt Lake City, where sales have nearly tripled each year since the company opened shop four years ago. General contractor Mike Peters got into bunkers (literally, folks!) after watching the TV show “Doomsday Preppers” on the National Geographic Channel. He was convinced he could build them better.

His underground shelters start at $59,000 and go way up from there. His top-of-the-line model has areas for raising rabbits and fish. The majority of his sales are in the $500,000 range.

“Almost everything I do is off-ground and located in the middle of nowhere,” says Peters, who often powers the shelters with solar panels placed on nearby sheds.

Customers “want a bunker right now because they feel the country is doomed after the election,” he says. “It doesn’t matter who wins; we’re in trouble.”