If you're looking for something cheap & functional, I'd go with a Wintec 500 Dressage saddle. They fit a lot of horses (unlike most cheap brands), they're pretty nice to ride in, and they're very hard wearing.
You can sometimes find nice used saddles for cheap, although it's very rare to find one of the really good brands in acceptable condition in the lower price range. Good brands to look for are County, Passier, and some of the older Collegiates. Steer away from Collegiates made in the last 5 years (they're made by a different company now), Crosbys, and Courbettes- they're all made with ridiculously narrow gullets (regardless of tree size) that just never works right on any horse.
Good luck in your search, saddle shopping is hell.
Of course, if you up your price range, you can always check out mine! LOL Balance International Matrix GP/Dressage Saddle - XX-Wide - C Seat - Havanna | eBay