The flex plan is $1/1000 messages: https://help.mailgun.com/hc/en-us/articles/203068914-What-Are-the-Differences-Between-the-Free-and-Flex-Plans-
No. It is not. Configuring SES is not for beginners. I’d recommend giving lightsail a try (which is for beginners and the standard install works just fine) with mailgun.
Again, if you need help with SES, you’ll need to find it somewhere else. There are also not really any instructions for configuring mailgun either. It’s on the service provider to make it possible to use their service.