Just to be clear, you are asking if the end use of a quilt influences where I purchase the supplies for a quilt?
No.
It is interesting, where I live the chain fabric store, Fabricland, has a quilt shop inside of it. So they sell their discount quilting fabric, as well, in a nearby section, they sell LQS brand quality fabrics. I buy more from the LQS side, as the colours, prints and fabric quality appeal to me. As well I frequent 5 LQS within an hours drive of my home.
Walmart does not sell much fabric in my town anymore, they just have a few precuts and they are coarse material, I would not use them for any project.
It is rare to find quilting fabric at thrift shops, but I have found a few pieces and picked them up.
Now what do I quilt?
Family quilts, couch quilts, pet quilts. If I am making a beach quilt, I would use the same quality fabrics that I use on a bed quilt or a gift.