The only place I've ever heard of a test cel is at Mandarake,
where they had several of them from Laputa for $60. I thought
long and hard about that, but quite honestly even if it 
/does/ come from the studio, in my opinion I'd rather save 
up and buy a sketch at the very least.
Even though it is xeroxed by the studio on acetate, I can't
get past thinking of it as just a xerox. I mean, the only 
thing I would do with such a thing is paint in the colors 
myself because a cel without colors is pretty dull, IMHO.
That would, of course, ruin any potential value it might have
for having been from the studio originally. 
So, if I'm going to just make a fan cel anyway, I might as 
well start from scratch, have a scene of my own choosing and 
save the $60. Or is it $100 on eBay? *sigh*
Just my humble opinion.
Ryochan
^_^