I am surprised that you have not factored into 
this rise in price to the simple economics of 
supply vs. demand;
or actually discounted it.
 When you say there are "no rare cels of DBZ", 
are you correct?  Such characters 
as "Gojita", "Mirai Trunks", and so on, only 
appear for a few episodes,(or movies) and then 
not the entire episode at that! Do you think that 
there are "large quantities of these cels still 
available?" That makes me happy if that is true! 
There "seems" to be definetly a limited supply of 
those cels (for sale).Where are they?? I live 
here in Japan. I can move both offline or online.
If you only tell me where this "large" supply 
of "Gojita" cels are! ;) I am not talking 
about "just any" generic DB cel.
 Like yourself and other sophisticated or 
educated collectors of anime cels may appreciate 
the quality of an AMG cel. You know the quality 
of cels, because of your experience with them. 
Many buyers still don't know or haven't seen 
anything outside of a TOEI cel to compare the 
difference! Those cels were cheap before because 
not many people had watched DBZ/GT in the STATES, 
But in the States it has only been out for a few 
years. So viewers and fans have increased 
exponentially, creating a larger potential client 
base. People who are now beginning to collect 
these cels on eBay don't know that the prices 
were that cheap a few years back. They look on 
YahooJp or eBay and think that is a reasonable 
price for the cels! In America, a Disney or Hanna 
Barbara, Batman cel is just as much or not more! 
So, in fact Japanese cels look cheap! 
The release of the series over satellite or cable 
TV in the States and I guess elsewhere is fueling 
the demand. People are deliberately driving up 
the prices I agree, because of the recent things 
that have happened on both YahooJP and eBay 
auctions. 
Most DBZ collectors, have seen what has been 
taking place recently, whenever a decent "Mirai 
Trunks cel",etc. has been put out for auction 
(and recently on dealer sites too)bids have gone 
through the roof! That's called "demand" if 
people are willing to buy at those prices , No 
matter how ridiculous it might seem, when this 
happens over and over again prices go up! It 
also, happens when dealers get on the bandwagon, 
a statement I agree with. And I didn't know that 
the on-line dealers in-turn are faced with the 
same price gouging. It's too bad. But this also, 
gives the appearance of short supply. It won't 
help the prices to come down if dealers stop 
buying and Japanese dealers raise the prices, 
maybe it is too late!!