[pizza234]

True, but due to the large extent of the services provided/required, it's very hard to know the unexpected costs, even if one has experience.

For example, one will hardly think of the cost of the disk speed (IOPS, in AWS), before moving to AWS. Then, they will suddenly have to deal with it (note that IOPS will be mostly opportunity costs, in case one doesn't choose provisioned IOPS of larger capacity).