Caught in traffic in New York's Times Square, Paul Archer watched the taxi meter climb to more than $100,000.

The tangle of cars and cabs and pushcarts was undaunting. "We've seen worse," says the 25-year-old from Gloucester, U.K.

Over the past 13 months, Mr. Archer and two college buddies, Leigh Purnell, 24, and Johno Ellison, 28, have...