Would the actual costs have been less, the same, or more, running on their own hardware? Processes can take longer running on your own hardware, but still have a lower TCO.
Possibly - the advantage of cloud is you don't need to provision for your peak load, it scales with usage from a few requests a day, to millions a second for an hour a day. If your usage is lumpy or growing fast then paying 2-3 times more than the cost of your own hardware can be cheaper.