A restoration depends on the quality of the source. For any of the release print copies that private collectors have i imagine it would be a bit pricey since these would be very "used" and degraded. This is moot though. Lucasfilm has many copies of the OOT, in both release print and IP form. There is no need to restore it. Lucas himself even has seperation masters from the dye-transfer technicolour prints and they are in immaculate condition. These simply could be scanned and digitally composited to create a digital copy of the OOT that looks about as pristine and high quality as the day it premiered. The cost of doing this woud probably be in the ballpark of about $100,000 or so, perhaps less, which really is absolute peanuts when you consider the importance of such an undertaking (and the millions in revenue brought in from the sales).