create a downloadable section on our existing online store

Hi, I was hoping you could assist me, i have recently added a page on our site whic we want to offer downloadable content. For example, This should be a section whereby we can upload a Music file to our servers, the end user would then be provided with the specific web address, a user name, a password and a validity perios, they can then log into a specific web address, say [login to view URL] , this would have the details about the song or band, and it will also have a section whereby the user can insert his or her username a password, once inserted the music file or pdf can then be downloaded. Specific options that we will need is: 1. we must be able to set each download product as free or at a price so we can sell online and offline. 2. We will need a section whereby each downloadable page that we create will have a unique id or password allowing access to the music file or document that we uploaded and set. 3. We should be able to set how many times the user downloads the files. 4. We should be able to set how long the user is allowed access with that user name and password. 5. MOST IMPORTANTLY WE SHOULD BE ABLE TO ADD A REMOVE THESE PAGES/DOWNLOADS FROM THE BACKEND/MAGENTO SECTION OF OUR SITE. EASILY AND AS WE PLEASE. I hope this make sense, and i hope we can get it done soon - I really want to get onto this .... please elt me know how much this will cost and also how soon we can get this up an running. thanks mike