I've gotten some very nice fabrics at WalMart for reasonable prices - that I think is comparable to some of the quilt shop fabrics. Although I think they may be discontinued from some of the "better" lines.
And there is some very flimsy stuff available that isn't much denser than cheesecloth/gauze. (Well, I'm exaggerating a little, here)
There is a huge difference in the weights of different fabrics - I bought a postal scale that will weigh in two gram increments - and I started weighing strips that were the same width and length. I thought that would be one way to keep all the fabrics more or less the same in a quilt I was making.
A personal challenge to me was to make a "satisfactory" quilt using only fabrics purchased from Wal-Mart. the pattern calls for 42 different ones. I think I have purchased the 42 different ones, but I've only used about 21 of them - sometimes it was because I chose the wrong color/design, sometimes the fabric was either too heavy or too light to go with the majority of the fabrics I was already using for this project.
Bottom line - if you know your fabrics, one can be selective and get decent stuff. I've noticed that WalMart also has some more spendy cotton prints that are quite nice. (Around $6.00/yard)