In addition to the actual daily cost of operation, you need to take into account the cost of the next 15 year/1472 overhaul, plus any intermediate repairs that will be required. Allocating these expenses on a daily basis will add substantial cost above those of just operating the locomotive.
A figure of $1,000,000 is often quoted as the cost of a 15 year/1472 day overhaul on the narrow gauge, and if every one of those 1472 days is actually used, you would need to budget $680 per day towards the cost of that overhaul. Operations that fail to reach 1472 operating days in the 15 year period would need to budget even more on a per day basis.
Michael Allen