I buy alot of them on sale. Hancocks of Paducah sometimes sells them for 3.99.
Some packs have different colors of a line, like blues and reds but they still go togather well.
I try to buy at least 3 packs of a line and that is for a lap quilt. Watch for how many squares are in a pack. Some are not worth the cost if there are less than 30 squares.