Do you scale to zero for the resume achievement or to actually save money?
My bills are around $0.02 a month from API Gateway =)
AWS Lambda NEVER goes down. And if it does, it's most likely someone messing with DNS or backbone routing again and half the world is broken anyway.
It does need skill though, the billing model isn't as clear as "you pay me X euros a month for a server, I don't care what you do with it", but it's not dark magic either.