Walmart has twin size sheets for $3.00. You can try Old Time Pottery by the mall. There are 2 Goodwill stores, one in Hamilton and one in Fairfield and the Valley Thrift in Fairfield. Might also want to try Bed Bath and Beyond. They can be fairly reasonable when you have a coupon.

Check Sam's Club. they sell bedding for motels etc.
Also ask some of the large motels/laundrys/
It is hard to find sheets made in USA
Is there a commerical laundry in the area?
Check garage sales/estate sales also.

if they don't have to be new call a local hospital and ask them where their laundry is done...