Eleanor Burns method is easy and dosnt cost anything.
You just use large squares and sew an x thru them. For 2 1/2 in you use two 6 in squares right sides facing, and you get 8 half sqs. Watch her videos on Quilters TV.
You cut in at 3 in on each side then thru the x that you have sewn on both sides of the x. For 3 1/2 use 8in sqs, for 4 1/2 use 10 in sqs. Then square them up and you have perfect half square triangles.