I'd suggest starting simple -- Get a rubbermaid type container large enough to fit your carboy/bucket in. Put the bucket in it, add six or so inches of water, and then put an old t-shirt over the fermenter so it hangs into the water. Point a fan at it, and you've got an instant swamp cooler, good for several degrees of cooling.
If that's not cold enough, fill the container with more water, and add a frozen water bottle or two. If you get 4 water bottles, you can cycle them from container to freezer as they melt and gain a few more degrees of cooling.
More involved projects include "Son of Fermentation Chiller" and a converted fridge/freezer with a Ranco or Love controller. Even more involved would be to excavate a basement so you can ferment year-round.
Seriously, a search should give you a lot of ideas. Here's an example