TMNT is one of my favourite games and a keeper for me.
TMNT is a really fun game, and there are a few around BUT you have to be careful because they have a original backglass instead of a translite so make sure that is in good condition, and the rear ramp area on most TMNT is worn badly, and u can see how much work the machine has done by looking at the spinning pizza graphic. (u can buy new pizza graphics to make the machine look newer anyway from ebay etc.

Overall, u want to look for a TMNT which has a nice playfield, a nice backglass and a nice cabinet. Expect to pay $2500 or a little more for a very very nice example. Hard to come by, very very good ones.

Pay maybe $1800 upwards for one which is a little rough here n there. Collectors keep real nice examples of TMNT.   Ninja NInja. Hope it helps.
Really really shop around.