I'm relatively new to cel collecting as well and 
have noticed the high prices.  I figured it was 
simply supply and demand.  More people are being 
introduced to certain anime shows as they are 
release=more people starting to collecting cels 
from those shows cels no longer availble on the 
market as they are already in the hands of 
collectors= more people after fewer cels=higher 
prices. (looks at what she wrote) Uhh does that 
make sense to anyone?  
Fortunatly I am lucky and obsessed with a 
character from an pretty much unknown and 
unpopular anime meaning there's not a whole lot 
of competition for cels from that show, so the 
prices are low.  And even when I lose out on a 
cel I can sometimes get another crack at it(I 
currently have a cel on the way that I lost out 
on on Ebay, AND I paid less for it than I would 
have if I had won )  
In a way that's also something for any collector, 
you may lose out on a cel now, but you may get 
another chance at it later. ^_^