I just hit a sale of clearance flat sheets at Wal-Mart. They were $2.00 for the twin and $4.50 for King. I bought several.
I use wide backing fabric for gifts and raffles. I use the sheets for utility or low cost (i.e. scrap) quilts.
I'm making a quilt right now for hubby and me. I'm using a sheet for the back. It's not for "good" but to use. When I make the quilt of my dreams, I will use wide backing and have it professionally quilted.
So, I'm both ends of the spectrum. (And I used sheets before I found out about wide fabric- never had a problem machine quilting.)