If you want to spend time in Edinburgh without the hassle of a car then the train would be a good bet. The trains are quite frequent if you are willing to change in York, a different but quite scenic route, or Preston. If you buy an advance ticket for a specific train, available about 90 days ahead for as little as GBP12, then the cost will probably be less than fueling the car. Try to avoid a walk up ticket as they are GBP96 even off-peak. TransPennine will allow you to take a train up to three hours later than the booked train if there is a flight delay.