I am looking for an inexpensive source of PMMA [poly(methyl
methacrylate)] powder that has a certain molecular weight.  I need a
sample with a known average molecular weight that is larger than
30,000 amu, but less than 65,000 amu.

I have found some suppliers of "polymer standards" that sell this
material, but they charge over $100 for 1/4 gram.  I am seeking a
source that charges $100/gram or less.  (We have found suppliers for
some other molecular weights as low as $0.10/gram.)

PMMA may also be called:
polymethylmethacrylate
poly(methylmethacrylate)
polymethyl methacrylate

Check www.polymersource.com.  They have several grades of PMMA, some
as inexpensive as $40/g ($32/g if you buy 5 g or more).  They have a
variety of molecular weights and polydispersities available.