If you want to allow your blog visitors to comment on blog posts you will need to explicitly allow them to do so.
If you want hosted sharepoint, this is the list. Take your pick. It all depends on your needs and I have just grabbed the prices of their site just to get you started. Your selection of a plan depends on how many users you would like to use this. In addition to that, how much space is required, monthly bandwidth, etc. Browse through the list. Pricing current as on today.