Just a heads up that Groupon currently has a deal for 50% off an Avis Car Rental.  $40 in credit will only cost $20.  The main restriction appears to be that there is a 2-day rental minimum (so you can’t use the credit for a 1 day rental), but otherwise it can be used anywhere in the US, Canada, Puerto Rico, and the US Virgin Islands.

The vouchers are valid until 12/31/2014, so you have a over a year to use it.  While rates can certainly vary, I do find Avis to frequently have very competitive rental rates.  Grab your voucher here:  https://www.groupon.com/deals/ga-avis-car-rental