for cooling you'll need air flow through the gh, for a cheap solution, you could use a diy swamp cooler if your humidity isn't too high..
your gb will act as a heat sink, insulate if you can, or cover with something reflective..
running a chiller would get pretty expensive.. when it got real hot here during my first season, i froze milkjugs full of water and used them in the ft... i had 4 or 5 1gallon jugs that i would rotate out during the day