Get the best budget rental car you can, but make sure it serves your purpose first. There are many companies competing for your business so if you book in advance (such as two to four weeks in advance) you should have no problem finding the car rental you need.
Budget car rental policies often dictate some specific items that you should take into consideration. For example, you may be required to bring the car back with a full tank of gas. If you do not do this, there may be a charge for that gas that is above what you would have paid for it.