If you're checking out your options online, you'll notice that most car rental companies offer two different rates: one for prepaying customers, and a higher one for customers who wish to pay when they pick up the car. My boyfriend and I are headed to Michigan to see his family, and looking at rental cars on Hertz, prepaying is definitely our best option. We could get a Ford Focus for $28/day if we prepay, but if we wait to pay in person, we'll be spending $34/day. For a three-day rental, prepaying will save us $20, and these savings get bigger the better the car you rent.