I owned a horse for 11 years, unfortunatly I had to put her to sleep in February. I agree that you need to watch for the things that sellers try to pull. Be sure to take someone along with you when buying a horse who is very experienced and can see these little tricks. Also make sure that you get the horse "vetted out" by a veternarian that you trust. My parents bought my horse for me and they paid $4500 for her, and that was after talking the woman down quite a bit. She had just turned 5 years old at the time and was a Palomino / Quarter Horse (the best kind ) You also have to consider the expenses of saddles, bridles, halters, blankets, wraps, grooming equipment, etc. etc. Horses are not cheap to keep. $275 sounds like a good board price, but what does it include?? Turnout? Feeding?? These are imporant things.
It sounds to me like you may be better off trying to find a horse to lease from someone for a while, this is much cheaper and a better way to get a feel of the responsibility of owning your own horse.
Sorry I rambled on for so long! I've been doing this horse thing for quite a while now, if you have any questions feel free to ask