Mine is either my Sega Dreamcast Kiosk(love this thing) only paid 50 for it and I sold my standard dc for 40 when I got it so actually only cost me 10.
Or its my complete copy of James Buster Douglas Knockout Boxing for the SMS, got lucky and found this for 40 at a value village.
Would love to hear about some of the rarities in your collection! Feel free to post pics too, I just haven't well because I am lazy.
