From HackerNews: Amazon lists the price of mac1 instances (running on rack-mounted Intel Mac Minis) at $1.083 per hour, $9,487 per year. You have to pay for 24 hours up front, after which they bill by the second. https://aws.amazon.com/ec2/dedicated-hosts/pricing/
They don't yet display any reservation pricing for mac1 instances, but they do offer a "savings plan." https://aws.amazon.com/savingsplans/pricing/
If you pay for three years up front, you can pay $0.764 per hour, $6,692 per year, 29% off. I believe that's the lowest price Amazon will offer you.
For comparison, you can rent an equivalent Mac Mini from MacStadium for $139/month, $1,668/year. Or you can rent their cheapest model for $59/month, $708/year.
You can also buy the equivalent Mac Mini for $1,899.