The main things I do are:
1. I don't worry about fancy backing. I use whatever is laying around. I piece chunks together. During covid, I even used sheets.
2. Same with binding. I use whatever is around, typically whatever is left from sewing the top. Rarely I will buy fabric for a binding (if it's a special gift).
3. I buy batting by the roll. If you quilt a lot this will save you a bunch of money. I also sew together batting pieces to get bigger pieces.