First to answer your question.  I've found that 
at ebay prices get undercut ... alot.  I've 
actually had someone ask to buy a Last Unicorn 
cel for $150 when it was worth $500.  Or better a 
Sailor Moon transformation for $175 when it's 
been sold at YJ for $400-500.  I think at ebay 
they think you're running a garage sale and don't 
care what you get for the cel.

On the other hand ... direct sales seem to work 
better.  And it seems that when you have the 
person make offers the better you get.  I've 
found that you either get what you paid for or a 
little more (which covers the paypal costs).

I'm sure the most reputable dealers have the 
sweetest deals.... especially when from time to 
time they offer cels at 50% (like Yann and 
AnimeChaos).  There are other dealers who set 
high prices who's stuff is still posted on their 
sites.

Okay, enough rambling ... bottom line, if you're 
not a dealer try direct offers.