Harmy said:

There's actually over 20 minutes, possibly half an hour worth of footage changed in the first movie alone.

Sorry, I meant changed completely, i.e. scenes that didn't use an exisitng element, such as the new x-wing shots, and the new jabba-han scene etc. and was only talking about Star Wars, not the whole trilogy.

I think there are less than ten minutes of footage that don't use the OT as the base-element, which means those elements were all scanned and cleaned up already, so the only cost would have been the few elements that were entirely replaced to be scanned, if they weren't already.