As far as I know there should be an option to transfer your PS3 account to the PS4 version for free when it launches, however when you do transfer you will not be able to use your account on the PS3 anymore. I would assume there will be a free download of the client on the PS4 at launch. If it follows what happened on the PS3 then if you already have the beta client installed on the PS4 it will just get updated to the release version.

Hope this helps