How much to have dedicated seperate mains spur put in is depend on how big the job is! ie How far between the fuse box to listening room, what kind of floor you have etc... I have been told by a friendly firm around here that it would set me back around £1000 for my place.
Therefore if you can get rid of the main niose by using aftermarket conditioner such as PS or Vertex you may save money (as long as products good enough).
The first thing you should do is get a noise sniffer (
like this one, LINK) to make sure that your main is producing un-wanted noise (which normally cause by other electric appilances that plug into the same main ring).