I don't know where you shop but Joanns carries mini bolts of basic colors like white, cream, red, navy, brown and black. Each one has three yards. I usually pick up as many as I have coupons for. They are great for backs, borders, plain blocks etc. At 40% off that comes to about $2.60 a yard. I make a lot of Linus quilts and they are usually 1 1/2 yds by the width of the fabric. Another way to get a lot of fabric for a great price is to purchase the wider backing fabrics 72" to 120" either on clearnace or with a coupon. I have a stash of that because I do handquilting for other people and it comes in handy for backs or it just gives me a lot of fabric because of the extra width. It comes in solid colors and even sutle prints.
Like most of the others have said, if you find something you really love buy as much as you can afford you will probably never be able to find it again six months later.