The T-shirt quilt is about the memories. You can not sell quilts and recoup your costs, much less make a profit, if you purchase premium product at regular prices. No one will pay that cost because they don't understand the costs. You don't have to buy Kona but I would not suggest something as thin as a Symphony solid. Purchase a Country Classic ON SALE and when you have a 20% or 30% off total purchase coupon. This can bring it down to $2.50 per yard. Same thing with your interfacing. As far as your batting and backing go, I made one quilt that I had a perfect cotton that I really liked for the backing and it felt a bit thicker, so I used flannel for the batting. Got it at $2.79 per yard and a 20% off total. It made a delightful and warm blanket. For quilting, I tend to echo whatever is on the shirt and do a decorative stitch winding down the sashing - very quick and easy. Remembering that your time is also your cost. But, no matter what you choose to do, you get it IN WRITING BEFORE you start. If the person is balking at the beginning, it will not end well. Because they are supplying the shirts, I have made them for as little as $60 in materials - then figure in your time.