www.craftsy.com usually has it on sale - today it's $7.15/1422 yard spool;
www.hancocks-paducah.com also has it at $9.47, which is a pretty good price, and they have a wider selection. You might look for Aurifil's sets at Craftsy; every once in a while I see the Mark Lipinski basics on sale and today it is $78. It contains a dozen neutrals in a nice box, which works out to $6.50/spool. These are the 50 weights, which is what I use for both piecing and quilting, and they have several combinations available.
Hope this helps!