Beyoncé and Jay-Z can roll in any car they want, but it’s hard to find the right choice. A Bentley? Too continental. A Rolls? Not quite enough room for baby Blue Ivy. No, this modern family rolls around town in ... a van.

That's right, a van. A Sprinter, to be exact, made by Mercedes-Benz and customized to the tune of $1 million. This big box on wheels has become the ride of choice for celebrities, business executives, and well-heeled families looking for something a little above your average Chrysler Town & Country.

The Sprinter, designed as a boxy cargo van for deliveries on narrow European streets, costs anywhere from $45,000 to $70,000 depending on factory options. Customers can choose between multiple diesel engines and a 4x4 version is coming next year. But what Mercedes offers is just the beginning. Custom work can easily run into the hundreds of thousands of dollars.

"We get these crazy, wacky ideas," says Ryan Friedlinghaus, founder of West Coast Customs, which has customized close to 100 custom Sprinters over the past few years. The sheer versatility of the platform leads itself to many different possibilities. "The cool thing about them is that they come empty."

Space and customizability are key here. With other luxury big rigs like the Cadillac Escalade, you effectively have to crawl to get into the back seats—not exactly dignified. With the Sprinter, you walk in and sit down. It's the Gulfstream private jet of ground transportation.

"It's the perfect canvas for anything that these people want to build," Friedlinghaus says. "Originally we were doing them into limos and then we had people wanting to sell cupcakes out of them or wanting mobile recording studios."

The recording studio, by the way, was made for Snoop Dogg. West Coast has also branded trucks for Monster Cable, and made mini-RVs complete with beds and toilets. These conversions can take a team of four employees two to three months to complete.

The team’s most outlandish project, Friedlinghaus says, was a canine limousine to take the pooches of the rich and famous to an ultra-lux boarding kennel. "We're always building limos for humans, so building one for dogs was something else." West Coast also makes a custom iPad app that controls lighting, shades, media, and other van functions.

West Coast isn’t the only option for those who want a gussied up Sprinter. Airstream, the iconic "silver bullet" camping trailer company, offers a pair of custom Sprinter models. One is tailored for the business market with connectivity and multiple seats. The Interstate EXT is made for posh families, with seating for nine and comfortable sleeping for two. Add in two TVs, a bathroom, stove, and leather everywhere, and it’s the perfect refuge from the rigors of roughing it.

The Sprinter is gaining popularity in the States. Mercedes-Benz USA has already sold nearly 9,300 so far in 2014, an increase of nearly 25 percent from the same time last year.

Unless paparazzi vanish from the planet tomorrow or leather suddenly goes out of style, expect to see even more stealthy cargo vans quietly moving wealthy human cargo around town in the utmost comfort.