500 cores is approximately 32 cc2.8xlarge instances (16 cores/instance). If you are running a highly utilized cluster, i.e. you are going for a one year heavy utilization reserved instance, the compute part is going to cost you ~$262,000. If you went with a 3-yr RI, it would be $183,000/yr.

Or to put it differently, ~$0.04/core-hr prior to any volume discounts.