Well, at minimum you are looking at re-pinning everything and rebuilding / replacing the power supply board. That is a Stern solenoid driver board, which isn't bad. But it isn't original and means someone else was in there before you. I hate repairing someone's 'quality' repair. I would absolutely make sure the AC voltages coming into the power supply board are correct. At minimum, you know you have a good transformer. The pins, rectifiers and fuse holders are going to be marginal. But if the AC is correct, the rest is obtainable and not very expensive.
Personally, I would offer $500. It is a good learning experience to repair and get up and running. You are going to put $300 into the machine between rubbers, bulbs, repair parts and miscellaneous stuff that comes up along the way.