Let's try and clear this up.
The basic iCloud service is free and incudes 5GB of space for Mail, Backup (of iPhone) and Documents (so far just iWork).
Additional storage is available: total 10GB, $20 p.a., 20 GB, $40 p.a., 50GB $100 p.a. (note that this is not iDisk-type storage for any type of file).
iTunes: downloading of already purchased items on other devices is free. Storage and downloading of personally added iTunes songs is $24.99 p.a.
Mail, Calendars. Contacts. Bookmarks syncing (though not displayed on the website), and Find My iPHone will all work with the basic free account.
'Documents in the Cloud' requires you to have the iOS iWork apps; if you choose not to use this the other facilities work perfectly well.