Go to the car rental page at South West Airlines. It lists and compares prices on the top rental cars. There is no charge to reserve your car. In the past I have checked back and a few times I have received a car for less. We have a FULL SIZE car for 7 days starting at $96.51 it is all the tax that ADDS to the total. The final total is $146.22 for the 7 days.
If you are interested, check out the link below
http://www.southwest.com/cgi-bin/carItinerary
Having fun Steve