Why dont you just get a aes? They have pretty good deals at the neostore, sure, $419 is quite a bit (cheapest one there) but it's gonna cost a bit in the end anyway...
(Then theres ebay, but I only buy from the neostore buttrock )
If I may, I have some good eBay recommendations. Try "search" then click on "by store" then on the bottom line, try "Bivari" or "game-baka-1dai". Those are some solid sellers from Japan, they almost always have good stock of NEO GEO carts, and the prices aren't too shabby. I've bought from both of them, no problem.
A couple of sites to check out as well: (Neogeotrade.com) and (Neoayato.com). Those two sites can be referred to by many members here, who have purchased from those sellers. The first is situated in Thailand and the second in France. They have good stock as well.
And finally, check out the selling/trading forums right here, there are always games up for sale, and theres many good deals to be found.
Just some friendly advice, as you can find the other games the neostore doesn't have available through other sources.
