Downloading Music for a One-Time Fee
Due to many legal issues with the artists that create music, no such websites exist. You may recall Napster used to offer a service called 'file sharing' which almost resulted in their demise.
Today you can purchase on a per-song or per-album basis, but nobody has been able to accomplish an open-ended subscription. It sounds like a disaster waiting to happen because friends would simply share one account to download thousands of songs.
There is also Rhapsody - available only in the US and its posessions. Go to Rhapsody.