The idea has been around since King C. Gillette first crafted his disposable razor: Hook customers by selling the main item for cheap and then mark up the price of blades.

It's a century-old business model that today's tech industry has taken to heart.

Hand out free cellphones, profit off the subscription fees. Lose money on each video-game console, earn it back on the games themselves.

But recently, computer printer manufacturers have come under fire for allegedly pushing the plan too far. Some customers and industry analysts charge that inkjet companies are using their influence to unfairly distort the price of replacement ink cartridges and shut out off-brand competitors.

"What I've found over the past few years is that ink itself is a very good commodity to be in," says Tom Merritt, executive editor of CNET, a technology news and reviews website based in San Francisco.

High-quality ink is expensive to make. It's packaged in specially designed cartridges that are difficult for others to replicate. And it comes saddled with patents and copyrights that the companies staunchly defend.

"But what's happening is that [printer manufacturers] have gotten so aggressive now in preserving their profits that a lot of people worry they are clinging too tightly to this minimonopoly," he says.

It's a concern that escalated into an antitrust lawsuit that was filed in Boston last month. The legal complaint accuses Hewlett-Packard of paying Staples $100 million to stop selling off-brand ink cartridges that are compatible in HP printers. Both HP and Staples deny any anticompetitive practices.

Despite the calls that the inkjet market stifles competition, there are still many alternatives available. One of the easiest ways to save a few dollars on the cost of cartridges is through generic brands.

"About 10 years ago, there were only about four places for a small company to buy generic printer ink," says Tim Molhoek, owner of O-ink, a small chain of printer supply stores in Michigan. "Now, there about 100 worldwide – the vast majority are in Asia."

These off-brand outfits often collect used tanks, pump them full of new ink, and sell them at a discount.

Another avenue to consider is refilling your own spent cartridges. Plenty of shops, from big-box stores such as Walgreens to smaller outfits like Mr. Molhoek's, run their own, in-house refill programs, with prices ranging widely.

For the do-it-yourself crowd, there are even take-home kits that let you squeeze new life into old printer cartridges. But this option is only for the adventurous.

"I tried one of the home kits," says Mr. Merritt. "But it just turned into a sloppy mess. I'll probably not use them again."

Similarly, the whole category of third-party inks comes with a big disclaimer. While the vessel is often identical to the name-brands, the ink inside ranges widely in quality.

Technology in every drop

Hewlett-Packard alone spends $1 billion a year on printing and ink research – a figure that no generic vendor could easily match.

This heavy investment is why ink costs thousands of dollars per gallon, printermakers say, and why they think consumers will stick to high-quality brands.

There's a lot of technology that goes into each ink drop.

"Typical ink development might have five PhD chemists working on it for several years, and of course an army of technicians," says Nils Miller, an ink and media senior scientist for HP. "And that was just to develop it."

In a process similar to making new pharmaceuticals, the lab teams build complex dye molecules, develop chemicals that affect the way the liquid spreads, and tweak the cocktail formulas for mass production, he says.

For several years, the independent reviewer Consumer Reports has warned against off-brand ink as a "false economy," especially with color and photo printers.

Studies have shown generic inks are more likely to leak or dry out inside the cartridge and run or fade on the page. And while the price per tank is cheaper, some generic cartridges run out of ink after fewer pages.

But for those consumers who primarily use black ink or don't need their prints to last, third-party tanks still hold great value, says Andy Lippman, a printer industry analyst for Lyra Research in Newtonville, Mass.

"Most people will never know the difference," he says. "It just depends on what you want out of it."

Outsmarting the printer

Of course, there are problems with genuine ink cartridges as well.

Just like gas tank sensors in a car, printers try to warn users when a cartridge is almost empty, but sometimes these sensors can jump the gun.

A study released this year, found that, on average, printers that use one cartridge for several colors say they're empty when about half of the ink is still left inside. The report, commissioned by the printermaker Epson, hoped to show the value of its method of using one cartridge per color. But the report found that even they run at about 80 percent efficiency.

"I've found that if you just pop them out and put the cartridge back in as if it were new, you can usually trick the printer into using the same one," says CNET's Merritt. "Or, if you really do a lot of printing, consider a laser printer."