The cheapest rates are going to be through the "University Flying Club".
http://studentorgs.utexas.edu/flying/index.html
You can get one of the 172's for as low as $95/hr and you will also see the 152's for as low as $75. I'm working on my PPL right on in a 152 and you don't necessarily have to be a member to rent a plane as far as I am aware.