Just check for wear (flipper drag) on playfield and make sure all the plastics look OK (some impossible to find). Don't stress about the Hunter ship or the Skull as after market replacements are available.
Have a look at the photos on IPDB (
http://www.ipdb.org/search.pl?any=terminator+2&search=Search+Database&searchtype=quick#2524)
That should give you a good reference point. If the game is not powered up, have a look (or get them to open backbox) and make sure all boards are present and not with holes in them etc..
Also check under the cabinet, look for swollen wood etc or signs of water damage.
Have a look underneath the playfield, again using the IPDB as reference photos to ensure all the mechs, motors etc are present...
Given the machine will be 'as is' ie no warranty, I would think between $2000 to $2600 max (inc the fees the auction house add on)....T2 is an excellent game and with LED's and a subwoofer make it an excellent machine.
