I think $125 is very reasonable.  Having worked in
a framing shop, I always get mine done 
professionally by a framer with animation cel
experience.  I've seen do it yourself tutorials
on the web, and I don't think the result you end
up with is nearly as nice.  

When I get my cels framed, I have a minimum of 
3 inches of matting around the cel on the top mat
and the bottom is usually another 1/4 inch.  
Any less matting just does not look as nice in 
my opinion.  Most of my cels are double and 
triple matted and that does add up.  I have a very
consistant look with my cels, so I always use the
same (expensive) wood moulding by Nurre Caxton.

I agree that if you use off the rack materials and
do it yourself, you can get off very inexpensively,
but the ability to go into a framer and frame it
exactly as you want it with the widest array of
materials available is worth the price.

To me, these are wonderful original works of art
and they deserve the absolute best I can give
them. :)

Just my 2 cents worth!  

Jen