The unpredictability of cost is actually the prime reason we stuck to our own cloud, where we rent (technically we buy the hardware that the company hosts, but it’s not really ours, we just use it till it breaks) the iron at a known rate. Which is just better for a public sector budget than paying by mileage, at least if anyone outside of the IT department bothers to look into what they are signing off on.
The really interesting part will be where we go from here. Moving from self-hosted to rented iron that we run our virtual servers on, was a fairly simple move that would be easy to reverse. The move into the cloud is even easier, but unless you’re careful, it could be very costly to get out.