I just checked walmart.com and for t-shirts and underwear there seems to be no difference on price, at least online.
I TAKE THAT BACK, some prices are different based on size...and some are the same. It seems that all are same except 2XL...does that sounds right?
There's always a little sign on the racks/shelves in my Wal-Mart: "Only $5.95 (Larger Sizes $7.95)" I don't mind--it's only fair.