I agree- check the used bike market. Craiglist (in my area anyway) is always full of nice buys $500 and under: I recently bought a Specialized EPIC FSR (XTR, Fox FLOAT front and rear, Discs) in very nice shape for $500... to reiterate previous posts, correct fit is key to an enjoyable riding experience so do not hesitate to pass on a nice bike if it does not fit well- there will be another one to come along that will fit. Your size is a pretty common one- medium or larger frame depending on the brand and how they measure- so your options will most likely be plentiful. An up side to buying a used higher quality bike is they have often been upgraded with nice tires, sometimes upgraded wheelset, stem/bars, etc. Good luck and welcome back to riding
