You don't even need the instance if it's a static site that can be served directly off S3. With S3+Cloudflare for a Jekyll blog, you can handle peaking to thousands of hits a second without noticing it at like $10/month.
It isn't made for that use case...the CDN provider I use takes ~15 minutes to update its Push Zone globally.
However, a pair of $5 VMs and loading comments via JS "solves" the need for dynamic updates since comments are the only thing likely to change frequently. Personally, I don't have much need for hosted comments so I don't bother.