J.P.
I use Expedia or one of the other deal sites. Priceline is a good one too. The prices will vary depending on the type of car and if you want to pick it up in the airport or get one off the airport property (they will provide transportation). It is much cheaper to get one outside the airport and the compacts are always well priced.
I have found that Alamo has decent prices and nice cars, Hertz has better quality cars but they are higher priced. Prepay for the gas it is so worth it. Then you don't have to worry about stopping on the way back to the airport.
FYI: Here in Orlando there are two gas stations near the airport and the last time I had to stop at one they were charging $5.00 for a gallon of regular gas. That was a year or so ago, but they take advantage of people.