Tip: go to the yardage store & buy some cotton flannel.
I recently bought 2 yds (36X72) for the princely sum--inc. tax--of US $7.98.
Out of this material I cut aprox 650 2x2 patches.
Be sure to wash the sizing out before cutting.
Id also recommend that you buy a cutting mat, straight edge, & pizza-like cutter. The cutting matt is self-healing plastic. These will bring up the initial cost, but it will not take you too long before you have the whole kit & caboodle paid for. They will also make it a great deal easier to cut the patches.