Actually, not much. Well, it depends on whether or not you have it sealed or complete, both of which I highly doubt you do. Just looking on eBay, there is one completely sealed that goes for $350, but I wouldn't doubt that's grossly overpricing it. There is one unsealed but complete for $150, but I think that's overdoing it as well since the other complete ones listed are about $50 at most, which isn't much when considering that's about how much it originally cost to get the game new. The cartridges alone seem to go anywhere from about $10-$40.
chewy || Petition to search whole words only on message boards: http://www.gamefaqs.com/boards/genmessage.php?board=7&topic=49840229
my cousin has an old video game store, and when she gets her hands on a gold edition [which is rare] she sells them for 30 dollars, i think. which sounds right to me, because ive been to other video stores that have sold the gray cartridge for $10-15, and for some reason ive only seen MM sold for 20$ and up. so considering how rare it is + how old it is, i guess around 35 sounds right. basically depends on the store, or the seller. theres no set price.
([-[[-dani-]]-]) *does an interpretive dance* DAAAANIIIIIIIIIIIIIIIIII!!!!! ~carr_mig