Hard to say if the legs are safe to attach. The block of wood glued into the corner with the threaded brackets could be compromised and attaching legs could do more damage to the cabinet. The front panel may or may not be easy to remove. Depends on how much damage is on the joints. They could be separated and it could come off with a little prying here and there. Or, it could a PITA. If, and only if, you have carpentry skills to replace the front panel and maybe part of the sides would I mess with it. It’s possible to cut away the bad areas and add in new solid wood, but this requires a fair bit of work. How much are they asking?

It sounds like you have enough skills to do the work if you need to. Its entirely possible that its still structurally sound, but have to see it in person to find out. If everything else is really nice, and you really want this particular machine, then I would at least try to get it for $500. There are plenty of people on this forum that can help get it up and running. If you get it, I would recommend going through and cleaning every switch in the game before trying to play it. If a switch is open, it should close, if its closed, it should open when activated. This also helps make it more reliable. Let us know what you end up doing!