Well I ask because reserved instances can significantly reduce the price of ec2 (up to something like 75%). Also just turning off idle instances can save a ton. If you invest the time in doing those things I think you can beat other options and so in that way, cloud infrastructure can be very economical.

It is like many other things involved in running a technology company. Investing in automation can pay off hugely.

The newer instance types are very reliable too (in my experience).