I know this works in DEN, so it probably works other places. If you know other places, list them out. If you rent a car in DEN, it is much cheaper to rent off site of the airport. There is a pretty large tax that the airport charges the rental car agencies for on site rentals. If you ride into town and rent there you can get sometimes 50% savings. Only downside I have found is the one I use doesn't carry many cars so if you don't like the car or want to change, it probably isn't going to happen. Also I noticed it was cheaper to call the office directly and book the car instead of booking it online. I usually rent offsite and return the car to the airport and get the savings.