You have some pretty fabrics there. I like your pansy fabric, but I am a fan of purples. I like the first and second batiks for your lake quilt and that floral you got on sale looks delish!!
I know how you feel about buying fabrics, it just does something good for the soul!!!
For my backs I usually try to find sale fabrics for $5 and under a yard and but 7 - 15 yards depending on fabric and price. I was able to get a ton of large pieces of fabrics from a store that recently went out of business. They used to have sales on holidays for $l a yard then $1.69 a yard. I have at least 60 pieces large enough to use for backings, in a range of colors and styles. I can usually find one of those to use on almost any quilt. They are all "regular" 44" width fabrics
Sometimes I will piece with leftover pieces as well or make a strip down the back with leftover blocks and such.
I am much more into piecing the tops as well!!! (that's why I have a lot of UFO's hanging around) I quilt mine myself, on my regular machine. I have not sent one out to be done, yet.