Search online for the best rates with coupon codes applied. Call another company up and have them beat the competitor price. They are all open to negotiation. If you are moving during a weekday you will also have more leverage.
+1 Penske matched the lower quote I received from Uhaul. The dealer threw a fit about it when I arrived to pick it up but I didn't allow that to become my problem. I went with Penske because of the quality of their trucks. Mine was newish (~50k miles)... Alignment was kinda off but I had an issue free drive from SW Florida to South Carolina. Will be using them again in a few weeks. Hope that helps.