I ran Minecraft on spot instances when we used to play in university, complete with automatic terraform+ansible provisioning and automatic saves/backups in S3. Never used Fargate but I doubt it can beat spot instance pricing. More than half my bill was network traffic.
You can set it to automatically adjust the price so it doesn't get preempted. The price used to be essentially at a constant minimum (m4.medium/large) during the evening & night when we played, so even without that we never got preempted.
I'm afraid this isn't completely true. You can still be interrupted for capacity issues no matter what your bid is. It's quite rare on more common instance types, but becomes a problem if you have more than a few GPU or high memory type instances.
They changed that a few years ago. It used to be the price would spike when they needed the capacity, oftentimes going higher than On Demand pricing. Now the price adjusts gradually, if at all, and they'll terminate instances regardless of bid price.
