I would try consignment stores and GoodWill in good areas. Back in SFO we got so much stuff cheap, new with a tag there! Now I live in a remote area, our Good Will or Once UPon a child has only washed out old crappy stuff that still costs 4-5 a piece or more! We do not have Old Navy in town. I do buy at Walmart - Garanimals has solid colors and decent quality for 3-4 a piece new. Target has some basics too and I buy it when they clearance it out (end of season) in the next size up for $1 a piece (e.g. solid colors turtleneck shirts). The Childrens Place just opened and so far no good deals, Gymboree is always expensive, Kohls/sears/jspenney never mark stuff down in our town... SO yeah it's Target or Walmart for us! Or the consigment stores back in San Francisco when we visit with family.
Gotta agree with the consignment and thrift stores in good areas. We live just north of SF and this week at Goodwill I scored a pair of Mini Boden cords, new with tags, for $3 ($38 on their website). I was practically jumping up and down with excitement.