True, ...but a general pricing guide could be 
made for anime cels. If you compare it to other 
collectibles that do have pricing guides (pokemon 
cards for example <--- How much are these worth 
now?) the market for cels is still much more 
stable. I'm surprised there isn't one for 
animation in general. If you were to add American 
animation with Japanese animation you'd fill a 
very large volume. The prices would be fluxuating 
for the reasons you've stated but there are 
enough generalities to make bi-monthly 
acessments...[ an A grade cel for a certain 
series with rare or popular character--range $150-
$200, higher for condition or scene ] This is 
done to some extent with baseball and football 
card pricing. Some players are popular all the 
time and some come and go.