i agree with jinx and drac--make sure you make a 
good offer.  nothing irritates me more than 
(usually ebay) people backtracking to our page and 
writing with a list of cels they want prices for. 
usually, if they're too obnoxious, we send them a 
list of ridiculous prices ;) (one wanted to buy 
almost every tenchi cel on our homepage--and 
seemed to think the magic number was $40!).

but when it comes to a collector who is seriously 
interested in a cel, trades and offers can be fun. 
And you never know how attached the person is to 
that particular cel!
good luck!
:)rosemary