Back to school clothing ideas to keep cool?

I live in the south and its hot to say the least. My school year is starting soon and I'm worried about keeping cool but still meeting my schools dress codes. The code states that we cant wear bottoms shorter then finger tip length, tank tops (sometimes if the strap is thick enough you can let it slide), and nothing all around too revealing. My school is basicaly a parking garage. No a/c in summer or heat in winter in the halls. Classes are pretty hot too. Any ideas of things I can wear and places I can buy them? Im an incoming sophmore girl! Im thinking sheer flowy tops with nude cami's underneath, airy crochet tops, etc. Im on a budget too. Thanks!