With Office 365, Microsoft is upgrading is current Online Services (Exchange, Lync, SharePoint) with the latest products version, introducing some new features.
Pricing (per user and per month) vary from $10 to $27, split into 4 different service levels.
To know the pricing and service level, go to http://www.microsoft.com/en-us/office365/enterprise/subscription-plans.aspx (in US Dollar) or http://www.microsoft.com/fr-fr/office365/enterprise/subscription-plans.aspx (in Euro)