You can find Twinnings and Celestial Seasonsings teas at most Coto/Disco/Jumbo stores, but the prices are still high (1-2 pesos/bag). I have never seen Tazo here (though it doesn't surprise me that Starbucks was carrying it), but Barrio Chino (Casa China) tends to have some good tea selections. Be prepared to try some brands you've never tried before. In any "regular" grocery store I'd recommend to stay away from the national brands, especially La Virginia, that's the worst!