Unlike an EC2 instance, though, these are going to be running on expensive, single-vendor hardware, and won't be able to take advantage of much higher-density b

Unlike an EC2 instance, though, these are going to be running on expensive, single-vendor hardware, and won't be able to take advantage of much higher-density blade configurations to decrease space, power, and cooling requirements. There's also the matter of a non-trivial per-image OS license cost from Apple. In other words, expect to pay a premium even over what you would for a normal full-time VPS, and don't count on hourly billing.