The dealers (don't know if the one you're 
referring to is US- or Japan-based) are going to 
have additional costs that factor into the 
markup.  Shipping, for one, especially if it's 
going overseas.  Not to mention profit, because 
obviously no one's doing this for their health.

The solution: people who want the cels that 
badly should bid seriously during the Y!J 
auction.  There are auction sites like Rinkya 
that will allow last second bids, even if the 
dealer tries to snipe the auction.  If people 
want the cel in question badly enough to outbid 
the dealer, then that's the end of it.  And if 
they wait until it's in the dealer's hands, then 
they'll have to know it's going to cost more.  

Of course, if they weren't willing to pay that 
much for the cel in the first place when it was 
on Y!J, then who's going to buy it from the 
dealer?  If he ends up with a lot of expensively-
priced cels and no buyers (assuming all buyers 
are Y!J savvy, which of course is probably not 
the case), that's obviously not good business 
practice, and he'll have no choice but to curb 
it.

It's still annoying, I know.