If you're willing to reserve the instance for 3 years, the average monthly cost becomes only $656. That's quite a good deal.
The only problem with reserving that instance for 3 years is that better hardware always comes along, especially with the cost of SSDs coming down significantly every year. Usually if you're in the big-data space, your hardware is likely retired after 24 months (12 months if you're well funded) so locking yourself in for 36 months might be a bad investment.