You may notice a difference in the piecing stage if you mix the lesser quality with the good stuff. I had one print that I got at Walmart that was a perfect match for a quilt I was making. It didn't feel as nice but the color was perfect so I used it. Everytime I got to a section with that fabric, it stretched and distorted a bit more than the other fabrics. I had to ease a lot of fullness in on that one print. It wasn't as noticeable by the time I got through, but I hated handling it. It would have been even worse if I had a different pattern with more triangles. Luckily most of mine was squares and I didn't have to handle it too much. I haven't bought any fabric at Walmart since that experience.
Once you get to know the quality of a particular manufacturer, you can shop online and get a decent price. I have bought the same names/quality online for $4-7/yd that I can get in the quilt shop for $8-10. I still buy at the shops too. I try to spread my business around a bit. I like them all and would hate to see any of them go out of business. :D