Another thing to note is with the rise of proxies and international bidders, prices are skyrocketing.
Recently I started using the proxy FromJapan to purchase some arcade hardware. Specifically, Namco System 256 and a Gundam game, I needed 4 sets for link up play. The current ebay prices where significantly higher when you'd even find one listed. The multiple listings on YAJ where 6500yen for a set(plus fees, etc) and even after the $250 in shipping, I came out $200 ahead plus I scored some random cheapy goodies. I think the "bargains" to be found are on items that in Japan are not valued much(aka pre-gouger). For example, Street Fighter II Hyper Fighting and Final Fight ask for 15000yen all day, which is around what ebay and forums ask for them, so adding in shipping and proxy, it's not a money saving deal.
Grand, I'd suggest go and browse YAJ and look for stuff you want. Get a idea of what they are asking for and getting. FromJapan has a decent front end to manage and watch auctions.