Call them. They will tell you the maxium that you will be reimbursed. Well, actually, not you but your son/daughter. They put the money into their Navy account. Since we were going with our DS, we decided to purchase our own tickets so we could all go together.
If you decide to drive from your home to USMMA, they will reimburse you just so much per mile. They do not reimburse you for the drive from your home to the airport. I guess they figure you can afford that since the education is almost free.