We are selling our daughter's used, 6-year old Britax Frontier 85 car seat. It retailed for $290 when new. Britax recently replaced the Frontier 85 with a newer name, which retails for roughly the same price.
This is one of the best car seats you can buy.
This seat has never been in a car that has been involved in an accident.
It is in great condition, no stains or rips, and everything works perfectly. It can be secured in the car using the seat belts, or even better, if your car has anchors for latches, you can snap it in with latches -- a breeze!
Here is a review: http://carseatblog.com/5751/britax-frontier-85-review-its-all-new-is-it-for-you/