Oh, it's expected costs.
Like, figure out the compute requirements of your code, multiply by the cost per compute unit (or whatever): boom, your cost.
Totally predictable.
Compared to suddenly having to replace a $20k server that dies in your data center.
So much easier.

Except when your code (let's be honest, the most likely thing to have an error in it... At least compared to some 4+ year old production hardware that everyone runs) has a bug in it that requires 20x compute.
But maybe that is a popularity spike (the hug-of-death)! That's why you migrated to the #cloud anyway, right? To handle these spikes! And you've always paid your bills so... Yeh, here's a 20x bill.