Space Invaders, Space Invaders Deluxe or Space Invaders II ? About $250-$400 from what I could find searching the groups, if you're talking about Space Invaders II (looks like a Pac-Man cocktail, not like a Taito/Atari cocktail) I'd say less for the older versions.
Warning: Just like Pacman and Gorf, the artwork was painted on the underside of the glass. This means 2 things. First, if the glass was scracthed, you'd have no way to transfer the artwork. Second, people scrached off a lot of the black above the control panel, and/or a lot of the art gets damaged from simple movement or the hot/cold cycle from use or (improper) storage.
so even though everything might be in good enough condition, you'd spend a good $50 on a new piece of glass if it's scratched and then an untold amount trying to replace/repro the artwork. Now if that is in perfect condition, then you've got a very good deal.
The rest of the cabinet is easily fixable and NOS replacement parts like control panel overlays I still see frequently on ebay and don't go for all that much.
The B+W monitor might be the hardest thing to find an identical replacement for if it is failing, but you probably could do a tube swap out of a consumer TV set just like color