A K-36 is also overhauled with paid labor, not volunteer labor. That is the single biggest cost of an overhaul. John Bush's estimate for overhauling the 168 is $650,000. A K-36, if it requires a new firebox, could easily hit $1,000.000. Restoring the 463 cost in excess of $1.3 million. Estimates for just the 1472 day work at $500,000 for the C&TS have been posted here by qualified people, but it is never "just" the 1472 day work that gets done. $500,000 is a floor, your mileage may vary.
Michael Allen