Sharing cars sucks, especially when the people you share it with don't take car of it. In my experience the best option to fix your situation is to just go out and get your own car. That way people don't take advantage of the hard work you put into the car, and you don't have to fight for the use of the car. Unfortunately you do have to pay for that privilege with gas, insurance, taxes, maintenance, etc. You will have to do it eventually, but I think it's worth the hassle.
You need to buy a transmission, flywheel, clutch kit, shifter linkage, pedal assembly, clutch cable, and the center console/shifter boot/interior stuff. Depending on where you go to get parts it should be around $500 for the parts. Once you turn a few wrenches on some cars it actually becomes a pretty easy conversion.
