Incase you have any qualms about buying from Lululemon, please realize that there are billions of other places to get less expensive, good quality yoga pants. I can't get over how gorgeous these Nike ones ($65) are.
Victoria's Secret and The Gap have a pretty sweet selection, too. Especially the sports tank tops at Victoria's Secret - they last you YEARS, it's weird/great. If I were you, I'd stay away from the super-cheap workout clothes from places like Old Navy and H&M since they wear out pretty quickly.