Ebay has lots of good deals. You need to research things like the difference between shimano xtr and shimano altus or sram "x" vs sram "y". I got a great 2009 shimano xtr light weight mountain bike for my son. Note 29 inch wheels (29ers) are all the rage now. This means 26 inch mountain bikes are going way down in value but are still great bikes. Lots of good info on youtube as well.