We try to help out a bit on this with Vantage which essentially gives you a DigitalOcean-esque view of your AWS costs. The first $2,500 in AWS costs are tracked for free which would seemingly cover your side-projects.
It sounds like you've found your home on DigitalOcean, but I'd be curious if something like Vantage would potentially change your decision to build on AWS? In particular what you mention about runaway bills is something that Vantage sends alerts on in advance. We also show you a full inventory of your AWS resources and what they cost you.