I have an slightly-off-topic question: If I want to test that my opensource project builds and runs on MacOS, what's the cheapest way for me to do this? AWS seems like a fairly expensive way do this at $15 USD per day
You don't need to leave the machine running (and billing) 24/7/365—turning it on for a few hours a day when you're building for it, or testing builds, should be enough.
It can be hard to justify $15.60 every time I want to test some random thing. Not to mention I seem to recall you can't actually cancel a reservation till the 24 hour window is up, so you need to remember to stop it the next day, or automate that action somehow.