The way I determine buying cels is buying what
I like and I won't pay over $150 for a cel from
a series with over 26 episodes if I buy TV cels
at all.  I mostly collect OAV cels such as Plastic
Little (one OAV, 55 minutes of footage) or Gunnm
(2 OAVs, total of 70 minutes) or Devil Hunter 
Yohko (approximately 5 hours of footage and no 
sign of more) I never paid over $300, but I don't 
buy for the resale value, I buy because I like it
but I do get angry if I feel I totally overpaid
for something (like a cel from the same sequence
sells for half of what I paid for mine) I feel
by buying from OAV series that were short and well
liked though my investment is better preserved.
I value my cels a lot more than a Tiffany lamp 
(those things are UGLY at times)  I think
the definition of fine art is art with no
 practical purpose (art, for the sake of art) and
I respect a lot of comics art and animation art 
more BECAUSE it had purpose.   BECAUSE it means
something to me, it makes me feel things in a way
a painting couldn't.  Don't get me wrong, I like
 art, I have Matisse and Monet posters up in my
house, but I also think Urushihara is just as
talented if not more so.  (his lines didn't get
as wavy and you can always tell what his stuff
 is ;)    )  
-Mel