A good choice for a decent quality rear sight is one from Magpul. They are perhaps a little more $$ than you are looking to spend; however, the quality is good (and less cost than some of the high end sights). That said, I have a set of Troy clone sights (found on ebay) that seem to be well built. For the 500 +/- rounds fired with these sights, I have not had a single issue. If I remember correctly, I paid $65 CDN shipped to my house. Another option is to watch the EE for a good used sight for a reasonable price (be cautious on the EE, many parts cost more for used than they are new).
Adam