I would have done it for $300 if only to try my hand at restoring. As Jediturtle said, "Not every machine needs to be a beauty queen." I was also told once, "you don't play the cabinet." That led me to a player's condition Judge Dredd that's been a blast. I've slowly been replacing my broken and missing plastics with used ones and enjoy the hunt as much as playing. Impossible to find NOS or Repop plastics for those, though I did recently score some NOS slingshots. I don't even notice the cab now. As Crazylevi said, "get it working as cheaply as you can." Then wax the hell out of the wear and start playing. You'll figure out the rest later. There are LOADS of BK parts available. There is a used upper and lower playfield on E-Bay now though it's not cheap at $379. There is a used set of plastics that appear to be in decent shape for $68. Replace your fuses. Make sure your power supply is working properly before you start digging around on your boards. You'll be surprised how much you can do on your own. Just my two cents.

Once everything is working electrically and emchanically, and you've addressed your concerns/desires regarding the playfield and plastics, I think if you're patient you'll come across a back glass. You can also get stencils to repaing the cab for $149.

http://pinballpimpstencils.com/?page_id=1316