Paul Elkins built a bike-towed micro-camper for $150 and has made the plans available.

From YouTube:

Paul Elkins fell for micro-camping in 2002 when he toured the country in his cabover "stealth camper". Sure he could make something more affordable, this year he began building a nomadic micro-shelter based on the Airstream design.

Using 4 recycled fluted-plastic campaign signs from a recent election, a $20 secondhand bike, 6 pine boards ($1 at Home Depot), screws, Duct tape and zip ties, he built his latest micro mobile shelter for only $150.

Calling it a "micro Airstream bike camper", it's a 60-pound "home away from home", complete with butane stove, bread-pan sink, counter, food storage shelving, clothes-storage bins, LED lighting, bed, windows, pee jug, bubble insulation, stereo with MP3 player, and a skylight made out of a 1 gallon plastic tub.