I have never rented a navigation system from a car rental, however, National does have a coupon for 50% off a navigation system. The only problem is that you can only use 1 coupon so you couldn't combine it with your $30 off coupon. Do you live near a Sam's Club. Ours recently had all there navigation systems on sale for $99. If your able to buy one, rather than rent, you can actually preprogram it before your trip. Good Luck!