I do sort of agree that spending that much money
on an incomplete cel is not "natural", but then
again, I have seen some auctions for Mayazaki
rouphs (gengas) go for $7000!!  However, I don't
look at them as fan cels.  They are part of the
production process as are gengas, dougas, and layouts.

Personally, I would never ever spend anything on a
cel that is missing paint.  If a test cel was
"complete", then I can see myself spending money
for it so long as I kknow it is original and I
would trust Anime Chaos on this.

Recently, I have gotten into collecting sketches.
 However, I also do not spend any money on partial
or incomplete sketches either even though they
offer an entire action sequence, etc.  
It is just my preference.

Star Phoenix