Relay rides

The biggest problem for most car-sharing businesses like Zipcar and car2go, is the cost of maintaining a fleet of cars, including paying for parking and insurance and staff to clean, refill and re-position the cars.

Relay Rides, a start-up that went live in June 2010, sidesteps that problem. Rather than provide cars, they connect car owners and potential renters and set the ground rules. They don't have to buy cars hoping people want them, and the car owners set the rates based on what they think their car is worth. The pitch: Owners can make money off their cars, and city dwellers who need four wheels from time to time can find cars easily.

Relay Rides facilitates short term rentals, provides insurance, and makes its money off a 40% commission. Most of that goes to paying for insurance, which is especially costly because Relay Rides is covering drivers with a wide variety of experience and driving histories (all are screened, and anyone with major violations in the previous 2 years is not approved).

A 2012 Fiat 500 Sport in Manhattan goes for $9.75/hour, $69/day, and $1,200/month.

Owners can expect to earn an average of $250/month, but a sample owner of a BMW 6 Series has cleared about $1,400 a month.

Relay Rides may be just in time for the sharing economy, because it's booming. Airbnb, the online marketplace for spare rooms, is on its way to make $1 billion a year.