Often budget companies are willing to do a free upgrade depending on what is on the lot at the time of rental and what they have booked. It never hurts to ask if you can upgrade for free or what other options they have for vehicles in the same price range if an upgrade is not possible.
When working with a budget car rental company it is also important for you to consider what the company is going to provide for you. Sometimes discount pricing, means discount service. Yet, doing a bit of research ahead of time will help you to determine what the company will do.
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.
