Use Williams AZ as your basecamp. It is a 60 mile straight drive up the highway to the Grand Canyon Rim. We have often stayed at the Circle of Pines KOA in Williams. They have a car rental connection at the front desk, we rented a van for our group. Williams is a small large town 15 minutes from Flagstaff, and I'm sure car rental will not be a problem at any location. You can take the tourist train up to the canyon. We haven't made that trip, spending a day on the train to cover an hour drive just wasn't our thing. Enjoy.