This was my experience exactly. Bought an alu-framed mountain bike for $45 as a beater, two sets of pads, one cheap chain, one sunrace cassette, one Tourney derailleur, one seat and post, etc etc. All-in probably $80 post-purchase but it's my daily ride now. Don't even think about going down this road if you don't do your own work, and don't buy anything you'd see at Walmart or CanTire unless it's crazy-cheap and you have a specefic idea in mind.