I have a 24 speed gary fisher mullet. I dirtjump but the problem is the front three gears are screwing me over. The chain falls off and bunches up and ive already taken one chain link out and im always tuning my bike. I wanted to take off two of the gears and put on a chain tensioner. When i asked the guy at the bike shop how much it would cost, he said it would be like 125 dollars for the tensioner and another 50 in service. He said it was because of the type of bracket i have. The whole bike is stock so if u can help me find one cheaper that would be great. Thanks fer the help.