i only shop sales, in person or internet. if i shop internet, i shop for no shipping, even if i have to spend over a certain amount.
when i shop sales, i shop with nothing in mind and i buy 3 yard pieces (remember, on sale with no shipping). if i have to wait , i do. but i don't buy backings until i need them. i shop the backings on sale also, but since i need 9 yards at a time, i wait until i need 2. then i wait for sales and only buy 2. i don't build a stash of backings. too expensive. the regular fabric affords flexibility for different designs, but the backings do not. i don't use sheets because i want the backs to reflect the tops.
EDIT: there's a fabric store in denver, pennsylvania, that used to have sales on their loading dock. they sold bolts that way. the bolts were so inexpensive that when they ran the sale, i would drive out and buy a few bolts. i went, i would say, every 2 years, and stock up. the store is sauder's. they have no email or mailing list so i don't know when or if they still have the sales. does anyone here know? please let me know.