I didn't read all the replies, but I'll just share what I do. When my boys were little, I made most of my own clothes and theirs too. My first quilts were all scraps from making clothing, and were just squares sewn together with no particular pattern. I agree, that batting and backing are expensive. I tend to only buy batting on sale, or with a coupon, although it is even less expensive to order online. For backing, I have used sheets (although some people advise against this), which turns out to be a little less expensive. As for batting, some people use old blankets, flannel, or fleece.
Thus far, I haven't made any show quality quilts, but they keep us warm anyhow.