Total up your supplies first, 2 fat quarters, cotton batt and cotton thread. I really can't see anyone paying more then $10 here and with your labor, I wouldn't think it would not be cost effective. I don't use my microwave bowls in the microwave. I just use regular 80/20 batt and put my bowl in after it comes out of the microwave. It really isn't one size fits all bowls either?