It's free if you only wanna post one pic and your ad will run for 30 days.
http://www.vehix.com/sell-your-car/
The Premium package is $29.99...you get to post 27 photos and it will run 90 days; then I think you can renew another 90 days for free. Somehow it's tied to other automotive search engines because the guy that bought my car said he found it on a completely different site. You should check it out...
In my mind Vehix isn't good for a 'quick' sell though, it's more about advertising your unique vehicle in a venue where people looking for unique vehicles will go; getting your vehicle out there for the 'right' person to find. In this case, the 'right' person is the one looking for a well-kept, lifted Hummer with performance mods. It's like one giant car lot. I never would have gotten my asking price for my Sky at a dealer or with a For Sale sign. I needed a buyer that was actually looking for my car, not one that just happened upon it.
As it turned out a roadster enthusiast in CA found it 'cause he'd been searching for a Sky to replace one he'd totaled. He wired me the funds and sent a truck to pick it up...