I'm way out of my league here, and only repeating figures given to me, but I remember vividly being shown the effect of corrosion on a Beaver prop by the pilot, and being told that a new prop was $27,000, with a useful life of 400 (?) hrs. Those figures may be slightly out but I remember being astonished that replacement prop costs were $65 an hour before anything else was taken into consideration. That would have been at least eight years ago now.