100% - $8 for a year, for most everybody not worth the hassle of doing anything else
I have no idea what overhead and other things
Amazon charges if you are just going to go EC2 on demand and shut it down.
So my suggestion is - do it that way for one month. Play every week, shut it down after, then spin it up again before your next game.
Then take a look at the bill at the end of the month, get the estimate of what a year reserved pre-paid pricing is, and balance it out knowing if you are comfortable with the level of effort that you just put in.