again approximately to the power 3
a B757 brand new would be what 75 millions
a straight-line write down over 10 years = 7.5 millions/year
for approx 35,000 hours
so +/- 2,150/hour
an old B757 including conversion is (say) 10 millions
a straight-line write down over 10 years = 1 millions/year
for approx 13000 hours
is +/- 750/hr
((mental arith is not in my limited assortment of abilities))
Plus limited use means relatively lower maintainance costs (takes a long time to get to he various checks)