Don't forget to look at tablecloths. Some pretty nice 100% cotton or real linen might be there. I used thrift store tablecloth when making embroidered bread basket liners---embellished muslin towels and sewed to squares of the tablecloth cotton.
Found some yard goods yesterday in my favorite church-run thrift store. Old because some of it still had G.C. Murphy Co. and Hills price tags. Plowed thru the box--some was really nice, some was 5&10 cent store quality and some thin and cheesy. I was able to find an armload and was charged $3. It's been a year since I found any fabric in that store. Be persistent.