According to the pricing page [1], a reserved Small is $69/yr plus $0.039 for any hour the instance is running, which could add up to another $341 for the year.
Good catch, I just quickly glanced at the figure without remembering the hourly rates still apply. Going with the yearly-reserved Micro you're at $128 for the year, which is a bit more than many shared hosts but at least you have absolute power over the software.
Just for a Jekyll blog, you could just host it on a free Heroku instance with an Nginx server and put CloudFlare in front of it.
In a free Heroku instance you have a lot of juice actually, especially for an Nginx server, the only problem being that the instance will go in idle mode after an hour of inactivity and so unlucky visitors can get some latency on the first request, although it's not that awful.
On the other hand CloudFlare is a pretty good proxy that works like a CDN, so with the right caching headers set, CloudFlare will serve many requests from its own cache.
[1] http://aws.amazon.com/ec2/pricing/