raeanna is right.....its not really a favour if you're charging for it. Im a firm believer in giving someone something over and above an agreed price in the long run, it may not be much but at its usually something that lets the person know that I DO appreciate their time.
If it were me (and since you're taking your wife) I'd just call it a day for a road trip with your gas/meals paid for and I'd do the favour and find someway to have some fun somewhere along the road
