Can't you just do something on your local machine?
There's stuff like dotnet new for .NET where I can just run that and have a skeleton project for a backend and I can start writing code immediately. I assume there's template creators for other languages as well.
My use case was a prototype for an iOS app I had in beta testing. It had a tiny but globally distributed user base, and serverless was a fun thing to learn on top of being relatively quick to set up. I'm sure if I had wanted to, some dynamic DNS and a small machine in my house would've sufficed. But hey--that's future decreases in cost. :)
If you're doing a prototype, wouldn't firebase or AWS AppSync be better options? You're going to lose a lot of time dealing with devops tasks (setting up IAM accounts, configuring storage services, etc.)
Can't you just do something on your local machine?
There's stuff like dotnet new for .NET where I can just run that and have a skeleton project for a backend and I can start writing code immediately. I assume there's template creators for other languages as well.