I used to work for Gallops Saddlery, The web's most exclusive tack store
and can vouch for their customer service and the quality of their gear. They work with National and World Class equestrians and carry a wide variety of used gear that is from good to like new condition. Their prices are very fair and they are happy to provide lots of information.
You'll likely have to email then for what they have in stock but it's well worth your time, especially in the price ranges you're looking for. They carry a lot of used gear like Stubben, Barnsby, Hermes, LB, Passier, and other high end saddles.
(edit: Sorry about the link, it named itself that! They also carry Crosby and Collegiate used as well)