T2 is one of those games that has funny pricing. If you look at ebay and the cost of the parts in one of those - 25" monitor - not cheap, Guns - very expensive and impossible to find, complete set of boards - $100+ easy, I don't really get why people value them for so little.
The bad thing about them is that the cab isn't really reusable - the display mounts in the back and reflects off of a mirror. Cool, but not practical for much anything else.
If the $500 game is complete and working, with great art and guns in perfect shape, then that might be OK if you really want the game. If it has screen burn, cracked gun cases, missing rocket buttons, etc, then you will have to spend a lot of money to get it up to snuff - assuming you can find the parts. The repro sideart doesn't match the original, and (like every other piece of art) is way overpriced. If you buy a cab for $200, and have to replace the art, and a few other pieces, then you're right back at around $500 anyway.
Just my T2 cents worth...