> my belief is that the cloud _is_ cheaper than on prem but it is difficult to configure it to be so.

It takes discrete effort in the core planning of your architecture. You cannot look at AWS resources (or any other cloud provider) as an all-you-can-eat buffet. You have to look at your requirements, look at the viable options that may support your requirements and take into consideration cost associated.

Without looking at cost during design your company/service/team will have a bad time at some point. There are also some really specific things you can do to lower costs but require knowledge and understanding of a myriad of technologies.