Our local coffee store roasts it's own beans, the green ones come in giant burlap sacks, and the owner saves them. I stuff one sack with a flat stack of about 20 of the others; and that makes a nice 3 ft x 2 ft target bag. I have yet to wear one out. Once a year when I wear a hole through the face, I get a new bag and just sack the whole target right up and it's like new again.
And they are sooooo quiet. Store-bought target bags are so loud in comparison. I can't stand the noise.