Airport garages occupy a dark space in our imaginations. Thanks to Hollywood, every multi-level parking structure reeking of jet fuel is seemingly a non-stop parade of international espionage, murder-for-hire deals, and cuckoldings in progress.

But what if airport garages instead were the backdrop for a different kind of commerce, an exchange that offered free parking, a free car wash, and free gas? What if instead of the price gouging we endure parking at an expensive airport garage, or the schlep to those cheaper lots so far away they practically require another flight, a smartly dressed valet waiting at near-term parking whisks your car away while you amble to your flight? That sunnier view of parking at the airport doesn't make for great movie scenes, but it might make for a good business.

That's the idea behind FlightCar, a Y Combinator startup just hitting the launch button.

Here's the catch with the faster, cheaper parking FlightCar is peddling: While you're away on a business trip or soaking up some sun in Maui, someone else is driving around in your car. In exchange for renting out your ride to FlightCar, you get the VIP parking treatment plus a free gas card. FlightCar insures your precious vehicle against theft, damage and liability, so you are less freaked out by the idea of your car being driven around by a visiting stranger.

The year-old startup is run by 18-year-old entrepreneurs Kevin Petrovic, Rujul Zaparde, and Shri Ganeshram, none of whom are even old enough to rent their own cars yet. Each decided to forgo college (Petrovic was accepted to Princeton, Zaparde to Harvard, and Ganeshram dropped out of MIT) to work on what they saw as an opportunity to connect people spending money on long-term parking and those paying to rent a car. "The three of us were frustrated that there are cars being purchased by rental car companies for maximum capacity, and at the same time there are car owners leaving their cars empty at lots when they go on vacation," says Ganeshram.

That frustration led to a way for car owners to rent out their cars while they're away, and for travelers to get a cheaper rental car, basically RelayRides meets a traditional rental car company.

Here's how it works at FlightCar's initial airport served, San Francisco International. First, you (the care owner) create a listing on FlightCar with your vehicle's stats, proof of ownership, and the dates you'll be traveling. On the day of your flight, you call FlightCar on the way to the airport and the company sends a valet to meet you at short-term parking to collect your keys. You catch your flight, and your car goes to FlightCar's warehouse, six minutes away from San Francisco International Airport. On the homeward bound leg, you call FlightCar with your return flight details, and a valet meets you with your car at the same parking area.

While you are gone your car can be rented to anyone who requests it via the FlightCar system. Depending on demand, you might get a renter or not. If you do, FlightCar will compensate you with gas cards, $10 per day rented for newer full-size cars, SUVs, pickups, and convertibles, or $10 per transaction for economy and compact vehicles. Whether your car is rented or not, you'll get a free car wash and free parking while you're away.

FlightCar provides up to $1 million in liability insurance for bodily injury and damage to other property, and up to $300,000 for damage done to the rented vehicle. The company also insures your car against theft up to the value of vehicle.

FlightCar also foots the bill if anything less dramatic goes wrong during the rental, including refilling your tank if the renter doesn't, compensating you 35 cents per mile if a renter drives over the 90 mile per day limit, and reimbursing you if a renter gets a red-light camera ticket while driving your car. FlightCar is betting its business model on these things not happening with unusual frequency.

Renters pick out the vehicle they want to rent during their trip on FlightCar's website, and make a reservation just like renting a car through any traditional car rental company. The selection ranges from Volvos to Hondas, with the most common model so far being the Toyota Prius (it is the Bay Area after all). Cars must be in good working condition, have no more than 150,000 miles, and not be made before 1999.

FlightCar verifies the renter's driver's license and driving history, and drivers with major accidents or moving violations are denied. Once the renter's flight lands, they call FlightCar and a valet delivers the car. Prices fluctuate based on demand, but renters can expect to pay between $15 and $34 per day for a FlightCar rental, cheaper than the lowest price we found on Kayak for the same time period ($37) and less than half as expensive as cars on Hertz and Enterprise, both which started at $70 per day. FlightCar pockets all of the rental revenue, and parcels out the $10 per day fee to car owners at the end of the rental.

What happens if too many eager car owners want to list their vehicle on FlightCar for the free parking? Ganeshram's not worried: "If that problem arises, we'll have to figure out a solution, but at the moment we have five times as much (renter) demand as supply." He's more concerned that people will be skeptical of renting their car while they are away and is counting on the free parking to entice owners.

That perk was enough to motivate FlightCar customer Andy Tong to list his 2004 Acura GL on FlightCar after searching Google for cheap airport parking. Still, it didn't calm all his fears. "It was a little unnerving to hand my keys off to the young valet, but he seemed legit enough to take the chance," he says. Someone rented his car while he was away and FlightCar notified him via email. Overall Tong say's he's happy with the experience because he got free parking and his car came back the same way he left it. "I would do it again," Tong says.

If you still can't shake the feeling that FlightCar is too good to be true, or at least the supply and demand equation doesn't add up yet, you're right. While FlightCar is eager for inventory, and therefore isn't hesitating to give owners free parking, there's a risk in the future that the startup will house cars that never get rented, cars that end up costing the startup money for all those the valets, car washes, and gas cards. Or maybe letting strangers from out of town drive away in your car is just too unsettling to gather momentum at all.

Ganeshram acknowledges the risks, but is confident in this smartphone enabled world where everyone is a supplier to someone's demand, it'll work. "The hope is that we can convenience people more while taking away the cost, so there's no need to ask a friend to take you, pay for a taxi, or take a two hour BART (train) trip," says Ganeshram.

If airport parking becomes something of a pleasure, Ganeshram and his gang of startup believers may even rehabilitate the seedy, expensive image it has. Even if a Hollywood scenario is visited upon your car while its being rented you won't notice, Ganesh jokes, since each car is thoroughly cleaned to remove all traces of food, pet hair, or wrongdoing. "And as long as the car doesn't get in the way of gun fire," Ganeshram says tongue firmly in cheek. "It shouldn't be a problem."