I've also run into a situation with obtuse/unexpected/excessive pricing. We were spiking a Mongo -> Cosmos migration and with our Cosmos configuration we were getting charged separately for each (empty) collection our app created.

Each collection was billed separately for provisioned throughput even though they were unused, and since the app created 50~ collections the cost added up pretty quickly before I noticed. Note: There is a way to turn this off afair, but the description of the setting made me decide to select it for a prod-like database.

In reality it's partly my fault. I should have kept a close eye on the costs until I was sure my mental model was correct. I also knew CosmosDB was just offering a Mongo API and wasn't actually hosted Mongo, so I should have been more vigilant about the differences in implementation. And of course I should have RTFM — although, even when I noticed the problem, it took me a long time and a support ticket to find the explanation in the docs.