When Inuyasha suddenly got popular, I suddenly
ssaw a LOT of auctions selling and actually,
prices for Sesshoumaru cels dropped at first. 
But, then, the amount of cels decreased and I
noticed that the decent sells are now shooting up
in value.

When I got into YYH, I first saw it on Adult Swim.
 Although prices for Kurama and Hiei selles were
high back then (and scarce), they appear to be
"stable" right now except for Kurama cels which I
have seen go drastically up since the Black
Tournament started airing.

So generally, when a show gets popular, the demand
goes up.  And as a result, the supply goes up to
compensate the demand.  So the prices tend to
"level out" at first since there is more
availability.  But, since cels are limited, once
the supply goes down and the demand remains high,
then the prices will increase.

Star Phoenix