Connecting threads sells precuts for the same price as yardage. I'm not familiar with the quaility of their flannel, but they have several nice looking lines and some in clearance. A 5" charm isn't going to make a very large block when it's ragged. I like seven inches with the cuts at 3/4". Could you use the layer cake and make your cuts 1"? Then you'd have 7" of pattern showing.
A 40 pack of charms contains less than 2/3 of a yard for price comparison.