Assuming your folks still sky subscribers then it should cost $80 to move house / "move the dish", and normally you give a cheque to the sky installer once the job is complete, and no "12 month period lockin" should apply.  Whereas if it's a new install it would be $99 paid to sky, and 12 month minimum sub.  The installer should get you to signoff on what was done (either phone line installed or not) and thus get paid by Sky accordingly (more for putting in a phone line!).  IMHO, I would have a live phone jack working behind the TV if you can, then all they need to do is put up the dish where you want it, run the RG6 from the dish to the TV, and you would be done.  If they are trying to extract any more money out of you from it being "A difficult install" then they are taking the mick.  When I had sky come around and "move the dish" onto our holiday home just before I canceled sky the installer ran in excess of 50 meters of RG6 due to where the roof <-> TV was and the cleanest way to run the RG6 was next to the existing RG59 for the UHF aerial.

One other thing worth doing while the sky guy is there is getting him to "upgrade" you to a new "small silver" DS230 Sky box, and blue smartcard, as the small silver box works a lot better (and is a lot smaller) and the blue smartcard changes channels faster than the old gold ones do (about 3/4 second faster).