Get a used brand name saddle. Don't buy anything new that is under $400, they are really crappy and won't help to put you in a good position. I got my HDR close contact (henri de rival) off of ebay used for about $400 (new is about $900), it has a medium tree and I'm really happy with it. Do some research first, go to tack stores and look at different brands new and used, feel the leather and sit in them to get an idea of what you like or don't like. You might even find a good deal there but I wouldn't run away from ebay or internet deals. You just need to know seat and tree size and what brands you like then start looking for something you can afford.
Do have a horse that is hard to fit?