Well, public transportation anywhere outside of a major city in the US is a pain in the rump. However, I noticed you said you would be in Georgia. If you would be in Atlanta, you can take their MARTA (rail system) to a large number of places. Granted, you do want to be mindful of your surroundings on any public transit system so keep that in mind.
Sure, you COULD buy a car for 3 months, but you are not likely to get the money back out of it when you need to sell it. I can't think of any dealerships that would be so flexible as to let you sell it back to them after such a short time. Perhaps you can contact the University you wish to attend to see if they don't have any ride-sharing programs?