I currently have 6 cels framed.  Four of them, I
framed myself.  First, it costs a lot less to
frame a standard size cel yourself (~$40 vs
~$100) using precut 11X14 mats and frames.  Also,
since you did it yourself, it's easy to change
out the cels.  I switch mine out every couple of
months to change the decorations and also make it
so that the same cels aren't exposed to light all
the time.  The frames that last month housed
Miao-chan, Sizer, Ifurita and Coronet now house
a different Miao-chan, Nuku Nuku, Fuu and Tomoyo.

The exception is when the cels are non-standard
size (or come with bg's).  In this case, it'll
cost about as much for materials as getting it
framed.  For example, I had the Priss/Linna pancel
below professionally framed as there was only
going to be ~$30 savings if I did it myself.