I used to be a high mileage driver and have always leased. It worked out well for me. Do not listen to people that do not know what they are talking about and say you have to purchase. Most leasing companies will let you pre purchase additional miles on your lease (around .10 per mile). Some will limit you to 25k per year (you did not mention how many you need). Check into leases that have lower mileage penalties at turn in. I think Toyota, Honda and Nissan are at .15 per mile at turn in-- others may be as well. In the long run this will be way cheaper than a purchase.
at .10 per mile an additional 10,000 miles is $1000 up front --so if you structure your 3 year lease to be 75,000 miles you will pay an additional $3,000 over a regular 15k lease. If you need more:
at .15 per mile an additional 15,000 miles is $1500 at turn in