a "Rough" answer needed here
The rough costs per year will be approximately that required to pay for the spare parts / life timed components / consumables etc. / engine overhaul ( unless already covered by an SBH / PBH type agreement, whch will need the cost to be factored in ), + VAT or whatever your local tax may be called depending on where in the world you have it serviced, plus the cost of the engineer(s)' wages, and not forgetting to whack on a load of profit for the maintenance organisation if there is one.
Then again if you just fly it for 99 hrs during the year in question it might not cost anything at all ( roughly )
