If the body and frame are in fair shape, for $400, I'd just drag it home and work on it at my leisure...
First, check the timing belt. If the belt is bad, Give the man the money before he changes his mind...
Check the clutch cable. Have someone work the pedal and see if it moves the clutch arm down at the trans. If the cable is broken, give the man the money before he changes his mind...
Does the transmission hold it in place? Put it in gear, and try to push it. If it moves easily, then the clutch is either completely shot or disengaged.
At any rate, $400 is a good price for a project vehicle. Even if you need to tinker it back to usefulness by replacing an engine or clutch, junkyard parts should make it economically feasible. If you are looking for a quick fix as a daily driver right away, you may want to go another $2K for one that is road ready.