agreed, they aren't difficult to maintain; however, the driveline is something which needs regular fluid changes to keep the transfer case clean. but, there is no way of telling whether the car has been abused and no way of telling when the transfer case can quit.
this is the expensive part. Control arms are also expensive. since he's pretty much said it's been overheating for a while there is a good chance the car needs a head. the rough running issue could either be vacuum leak (usually the intake bellow-black elbow) or it's been overheated so bad the motor is running like crap. unless you have experience and know what you're doing stay away. if you're handy it could be a good car once it is diagnosed and fixed.