One of the best things about the cloud is the ability to spin up new infrastructure for your dev environment. You can have a completely isolated environment for a new branch that you're working on, allowing you to test your changes in isolation.
This is fantastic as you can speed ahead on changes unencumbered - the only problem is that you'll leave a trail of cash sitting in your cloud providers pockets, which often doesn't work out so well for your business.
To attack our cost blowouts, we started a side project in our lunchtime to figure out how we can stop the hurt, and came up with Batman built using Serverless. Most of our infrastructure is managed in a single place (cloudformation) with a set of tags associated with each stack including the slice (or branch name), and the cloudformation stack keeps a created date & last update date. Utilizing this information Batman runs every night to cleanup stacks that are on non-master branches where the stack hasn't been updated for 7 days. This is usually enough time for us to have tested the branch and integrated it into the master stack.
We've also recently added a webhook trigger that deletes a stack when the branch is deleted in git which saves us up to 7 days of running costs.
We've stopped over 300 stacks in a month, and at a guesstimate of $1 per day running costs for a stack, the dollars quickly add up.
There are many ways to save costs, and we've found that for our journey into AWS, Batman has come about at the right time. Not only has it been interesting to explore serverless, our team got to do a lot of the work with some mob programming which was really fun (more to come).