Quoted from Ssurly:
Very helpful comments and replies -
It simply does not come on at all when connected to power. No corrosion damage. The gentleman selling has early onset dementia, the family wants to sell off some of his larger items as he is getting ready to move out of his house. They have NO IDEA what to sell it for and I have no clue what I should offer.
Yeah, I mean a totally completely dead game could just be a blown line fuse by the power switch. Easy and quick to change, and that could get you more info. I think they're usually an 8a slow blo.
Otherwise, the power supply could be totally fried. But I'd be doubtful that it would be totally gone to the point where nothing lights up or happens on a power-up. If it is just the line fuse, then that's a very quick, easy and cheap fix.
Even power supply boards aren't too expensive in the grand scheme, at least for most games. But you can't really diagnose much when the game is totally dead like that. Short of just checking fuses and looking for obvious damage.
Offer-wise, I say $1000 to $1500 is fair. I think Batman Forever's average-price is like $2500, so that gives you $1000+ of wiggle room in case you need to buy new boards or displays, and your time of course is worth something. And who knows might not be very much wrong with it. That's probably what I would do.