Welcome aboard, Kendra!!
To answer your question - you need to consider some other questions first -
If you want each block to have different fabric - there are 225 blocks which includes all 169 squares, 52 triangles, and 4 corner kites. I have no repeated fabrics [actually I do have one!] in the blocks but I have used the same fabric in a block and a triangle. A FQ measures 20 x 18 - you need no more than 1-2 5" charm squares for the print part of each block. 20 x 18 will give you 12 5" squares and a 3x20" remnant out of which you will get more .... I figure you can get 8-10 blocks out of each FQ [you will need an equal amount of background as well.]
I guess to answer your original question - 20 FQs will give you enough print for 160-200 blocks, with lots of repeated fabrics.
If you want more variety, my advice would be to buy a couple of sets of charm squares - KQ has a set of 40 for about $13 a pack - you will need to order two packs, which will be more reasonable than ordering the 10" squares, but you could do that and each square should give you enough print fabric for a square and triangle.
Other sources for CW fabrics are:
http://quilts123.com and
www.reproductionfabrics.com
hope it all helps!
Gus