I'd like to throw in my $.02 if I can.. :P

It also depends on what else is going on at the 
time I would think. For example, I expect that 
AMG cels are going to go up in price once the 
Megami Movie is released. By how much who knows.  
Cels from this show are already expensive 
depending on the character.  

I'm not sure that Nadesico cels went up in price 
either after POD was released so I could be 
completely wrong about the above statement.  I do 
know that Nadesico cels are pretty expensive for 
the female characters, especially Ruri.