By "turns on" I assume you mean, doesn't boot and won't start a game. How much work can you do yourself and how nice do you want it to be when you're done? Expect to need board work and/or replacement on several if not all boards. Not knowing more than what you posted, I'd say $500.

More info and/or pics will get you more accurate info.

Also, you did fine, for your first post. Welcome!

Buy it!

Must have missed a Zero in there....

Where do I sign up to find $50 Xenons? LOL

Buy it, its worth $50!

& welcome to Pinside!

What they said.

That's crazy, I wouldn't pay less than a $100 for it.

Welcome to Pinside!

for $50 it would already be in the back of my truck and headed home.

There is a tone of help on this site that will help you get it going or take it off of your hands if you don't know what to do with it.

load that thing up ASAP.

New playfields are in the pipe from CPR, that'll run you about $800... not sure if they are doing or have done plastics, those will run you another $150ish. The tube on these are often shot you may need to replace that. Cabinet stencils another $150ish. Depending on the shape of the boards you may need to do some work there, you could pretty easily put $1,500 - $2,000 into it to make it look beautiful. As far as early 80's Bally's go it does have some desirability... behind titles like Fathom/Centaur/EBD but ahead of titles like SBM I'd say. $50 is obviously a complete no brainer, get it loaded in your vehicle stat!

"turns on"... "plays properly"

There is a huge distance between those two terms. The machine is worth $50, assuming you do not have to pay to get it home and pay to store it, and also pay to have it fixed.
If everything is there (cabinet, playfield, backbox, boards, backglass, power supply, coin door) and the game lights up but won't boot it's still probably worth $500. You could spend $2000 if you need new boards, new playfield, new backglass, new cabinet decals and can't do the work yourself. Still could sell it to someone and get your $50 back.
Condition is king! Water damage? Battery alkaline damage on the boards? Playfield worn to the wood and/or planking? Rust everywhere? All bad signs that will cost various amounts to fix.

50 bucks is a steal. If the backglass is in decent shape you could atleast hang that on your wall

Unless it’s actually on fire right now $50 is a steal.

$50? BUY IT! I drove 10 hours last month to get a working one with a beat up playfield, nice BG and cabinet. I friend in Ohio just snagged one for $500 last week non-working with a nice playfield and BG. You can't lose. I'd be driving there now.

As far as costs to fix it, if you're just interested in making it look nicer, plays and not a be show piece, it can be done for under a grand with skills you can learn on the go. That's assuming it's complete, cabinet that will hold legs and the wiring wasn't butchered. Xenon is great player, I've had one for 18 years. Just a got 2nd just for the cabinet.

I drive 12 hours round trip to pick up a non-working Paragon where 90% of the art peeled off the backglass. That game was $100.

If you don’t buy this $50 Xenon it’ll be a huge mistake regardless of what condition it is in. Buy it and start an article on Pinside “Help me restore this $50 Xenon project.” A lot of people will help walk you through the restoration process even if you just want to get it up and running in player condition, not a full restore.