What you're willing to pay I guess.  Dealers expect anywhere between $2800 to $4000+

Private $2000 (as is) at the low end to $3500 for a mint one.

http://www.pinpedia.com/machine/Revenge-From-Mars/prices?c=au

Hard to go by Pinpedia's results as you don't know whether they are 'real bids' or not.