Azure has a habit of charging me more than I expect. Neither AWS nor GC does that and in both of the latter cases I'm either fully aware of the costs, or it's lower than expected thanks to the moderately generous free tiers, which I usually fall under.
But Azure is different.
During a workshop I used an "integration account" which costs staggering (about) US$30/day. To be fair, it's for enterprises, so it's actually not too expensive for what it does, but I used this by accident and it consumes all of the US$200 of have-fun-and-play-with-it in 7 days. I was not even using it for 6 of those 7 days.
The second time I try the very good Build a serverless web app in Azure. I like it a lot. Instructive, with command line instead of mouse clicking. Really nice and highly recommended. It's using a Dynamo DB database. I use 170 MB at 100 RU/s. That's 5 Yen in total for storage (no issue here), and 96 Yen per day for the reserved capacity. Does not sound too bad, but it's 3000 Yen (about US$30) per month while not using it.
AWS does have some tricky items too (load balancers, RDS instances, RedShift etc.) which costs, but I am aware of those and avoid them if I can. Google is usually cheaper than expected and I never had a negative price surprise either.
But Azure...twice they got me. There will be no third time. I'll have to learn their costing model before I'll use Azure again.