-1 datadog. Unless you have an SRE on payroll, it's obtuse, expensive as hell and you can never tell what exactly you're paying for. I don't like it much. It took a LOT of man hours to set up.
Get on the phone with them. I setup regular calls and had them explain each and every charge and where it came from. They would even waive billing on a feature i wanted to try out so i could determine baseline cost. I 100% agree the pricing is impossible to understand but they will work with you to find what works from both an ops and budget.
I have to object on the lot of man hours. This was by far the easier thing to setup compared to all the competitors and the open source solution we have. Maybe a week or two to setup everything on all our hosts and capture all the metrics for systems and AWS and databases and custom metrics.