Hello,
Alfresco Community can be used in production environments. A lot of users in SMB range as well as institutional users (i.e. scientific, cultural or non-profit organisations) have used Community in production for several years. This includes e.g. Spanish National Library and CERN.
Alfresco One was charged purely on a per-processor basis up until 2013, but now a primarily user-based model is in place with per-processor pricing only for some addons / opt-in elements. The Alfresco One price model lists a 300-user installation as the smallest option, which means that it often is not an affordable option for SMBs. But Alfresco also provides a cloud-based service starting at 50 users which provides the same core functionality and avoids any additional costs (in hosting / infrastructure) that an on-premise installation entails.
Unfortunately it is difficult to give even a rought idea of the cost as the new price model also includes far more flexibility for custom-designed price constructs / discounts than the previous one. Also, any comparison against SharePoint often moot as Microsoft too may be giving ridiculous discounts to snatch up a particular customer.
Last I checked, using rather pessimistic list price models of both, Alfresco One offered about 10-20% savings on a per-user basis compared to SharePoint (not including licenses for additinoally required/related Microsoft infrastructure products).
For a better comparison you should really talk to an Alfresco sales contact.
Regards
Axel