I buy 108" backing from Marshall's for under $8 a yard. Lots of colors to choose from and under $5 a yard if you buy the bolt. To buy a bolt call and order from a rep. I use Sharon. No tax number needed but you can only buy MDG fabric line wholesale if you don't have a tax number. Check out Dream Cotton wide backing for nice solids.
https://marshalldrygoods.com/shop/fa...quilt-backing/