The prices are about comparable to Ebay over here but it gets into more $$ when you factor in the cost of shipping them back home. For example, the Dig Dug II "kit" is about $380USD. There was a Crazy Climber 2 PCB that I just saw a couple of weeks back sell for ~$350USD and one jsut sold on Ebay the other night for $325. There are exceptions though as the Japanese collectors have their own idea of what games are grails and there are items over there that go for high $$. I've seen Missile Command PCB's sell there for like $1100USD.
You really have to want something or it has to be fairly hard to find here in the US to be buying it over there and paying the shipping to get it back here.. The NZS PCB I bought I could have probably bought over here for a little less than what I paid for it, but it included all of the paper extras like the manuals to make it worth while for me to pull the trigger on. The Monkey Ball CP is fairly hard to find, so I figured that I would grab it as it might he harder to find the CP than the Naomi bits needed to play the game.