Do you have a friend who is a cyclist? If so, that would be an invaluable asset is selecting a used, good quality mountain bike. If not consider a Nishiki from Dick's; these would normally be low quality bikes, but are assembled (including having the wheels built) by the Detroit Bicycle Co in the US AFAIK) Some may denigrate the China-made frames, but I've had good success with those from Bikes Direct which would be another good source, but seem to be depleted of many styles.