Well, Ghibli cels are expensive.
I think they are one of the most expensive cels 
out there.
They didn't officially released the cels, so the 
cels which are out are just a few after my 
knowledge.
I only have one Mononoke cel, I'm very happy I 
got it, it was more expensive than the price you 
mentioned, but I heard of Mononoke cels going 
away for $8000...