Christy,
The 500 this thread was started about was like yours, missing lots of parts and in need of a lot of work. It cost us some money although I don't know how much as well as the cost to get the parts.
The other 500 was free. Got it from Freecycle. Lady didn't know what she had. It didn't need any parts but needed lots of cleaning and TLC.
They are worth it. I'd rather refurbish a 401a or a 500a than touch a new machine.
Joe