Those cleaning disks don't really help much. They only clean the center of the "lens/eye." A technician can get in there with a swab and remove all the dust and accumulated oils from the lens.
The cost, the last time I had one looked at was seventy nine bucks to open it up and that included a cleaning, but nothing else. If there is actually something wrong with the unit, the repairs would be more.
I have had excellent luck with scratch removal services, though, like Randy mentioned. I often buy used disks of rare items and sometimes they are scratched. Things I get from the library are often too scratched to play properly.
The guy where I work said they use one of the forty dollar "Disk Doctors" off the shelf, nothing special to it.