AWs is pretty bad at telling you how much something you're not running will cost if you run it but I've never had any issues knowing what something has cost me in the past.
>Go to the AWS console and try to answer even simply things like how much did the last hour/day/week cost me?
Click user@account in top right, click My Billing Dashboard, spend this month is on that page in giant font, click Cost Explorer for more granular breakdown (day, service, etc.), click Bill Details for list breakdown of spend by month.
>Or how about some notifications if that new service you just added is going to cost vastly more than you where expecting.
Billing Dashboard and then Budgets.
edit: This assumes you have permissions to see billing details, by default non-root accounts do not which might be why you're confused.