The "omg my bill is out of control" issue is usually manifest from a few sources, one of the biggest is relying heavily on custom metrics added over time, and so you think you're paying X but really you end up paying 2-3X or more by the end of the year. But the tricky thing is, most of those things that cost a lot of money either have a lot of value, or held a lot of value at the time.
(I work for a Datadog competitor)