Hobby Lobby online has the heads listed for $9.99. However I could swear last time in to my local store I saw them priced several dollars less, and that was without using the 40% off coupon yet. Of course if you don't have a store near you doesn't help, but if you do might be a source. I'll try to stop in this week and report back.
Bert, it looks like there's a Hobby Lobby in Tacoma near Routes 5 & 18.