I sold antiques for 30 yrs, and feed sacks were used by feed stores as late as the 60's and 70's. Take note of the colors and the trends during the yrs. If you think of them as yardage the price would be high but as feed sacks not so much....I sold some that were not exceptional for 5- 6 dollars each. Yard sales and estate sales may be a better option. Special ones commanding higher prices were figurals, especially black Americana and other unusual scenes or motifs. I have four sisters and when we were young in the 30's and 40's, we would show our Dad what feed sack patterns we wanted and that we needed more of those. As I remember Mom buying yardage in the store, it was 25" wide for 10 cents a yd and later 25 cents/yd for 36" fabric. She often called it material. I was born in the middle of the dirty thirties and cannot imagine the struggles my parents endured in Western Kansas at the time. There is nothing about that time I would want to go back to. When I married my husband, he took me to see his aunt who lived in a sod dugout in the early 60's. But, mercy me, she had a piano and fiddles and good solid furniture in this humble dwelling. Her husband might take one of the children to town with him on his horse and be gone a week before she heard from him. That was some of the Old West I remember.