this case, I had to figure out the going rate for car rentals on a particular date and specific car size. Since we are bringing the two kids, we wanted something with a bit of luggage space.  In my experience, Expedia usually has very reasonable car rental rates, so it's a good place to start.  After that, I typically cross check the prices with the car rental company websites.  It usually works out that Expedia is cheaper than the direct website. 2.  Get Auction Prices As mentioned, we were looking for a particular size vehicle and in the city that we were looking, it meant only a couple of vehicle types to choose from.  As we were comfortable with both vehicles (ie. luggage capacity with decent gas mileage) choices,  auction sites like Hotwire and Priceline can work well in this situation. Hotwire works by offering the user a low price, but the user can not choose the company, just the vehicle size.  I assume that the car rental companies bid their lowest rate to Hotwire on a daily basis.  Knowing that, it's best to watch the vehicle rental price over a period of time as it will likely fluctuate daily.  Before moving onto the next step, I usually wait until the car rental price has plateaued for at least a week. 3. Bid your Price! Now that you know the going rate, and the lowest price that car rental companies are willing to accept via Hotwire, it's time to use