This question is kind of impossible to answer. It depends on what type of car, number of miles on it, how it was treated over it's lifetime, how good the work done on it before was, how well it was maintained, how you drive it etc. And it just depends on the car too. You can have really good luck, or really bad. Some jobs are definitely worth it to do it your self (changing your oil, lights, welding the exhaust, etc.) but others you can't do with out a lot of skill (head gaskets, fuel pump, certain valves, etc.) and some you can't do at all without really heavy duty machinery (struts).