After overhaul you're aircraft is not completely new. You have to depreciate if you want realistic figures. On the other hand the prices on new aircraft go up all the time and after 3 years the worth might be the same as you paid.
We don't depreciate in calculating the hourly cost. However I count 10% of the invested money on a yearly basis as interest (so being cost really). If we'd invested that money differently we would make about that as well.
So investing $400,000.00 means I have to add $40,000 to the yearly cost.