There are a lot of good used bows out there- the classifieds section of TexasBowhuter.com has always got some for sale. The first thing you need to do is find out what your draw length is. Buy a new bow and they will fit it to your draw length. Buying a used bow you will need to know your draw length. There are lots of folks that have to have the newest, latest, and greatest bow every year so you can get some good deals on already rigged out bows that will only be a year or two old.
On the subject of draw length...go find a Pro Shop or ex-competition shooter turned PRO SHOP guy to help determine your draw length...DO NOT go to sales store (employees may or may not know the correct way to determine draw length)...When I started, I had several different folks tell me my draw length (sales store types) and I could shoot, but not great...years later, when I went to a Pro Shop and told them my draw length, they insisted on taking through the process again...when they set me up with a bow in the correct draw length, it was like someone turned the lights on...and I could shoot lights out! Just saying, go to a PRO SHOP to determine your draw length...then go buy whatever setup you can hit with consistently...