In Surplus...
Look for sanding belts (Norton)
1 X 30", 4 X 24", 4 X 36" all for $1-2 each, in 50 and 80 grits.
If you are a dovetailer, they have 1/2" D/T bits for $2 also.
That 4 X 24" belt can be easily ripped down to 3" if you have a Makita, etc. and still have a 1" strip left over for...