At the risk of boring. The cost of the Chinook and crew is unknowable. If they were not doing this repair, they would be doing normal exercise and training. You cannot easily calculate the cost per hour of items that are budgeted per year and NEVER intended to be sold by the hour. That's not what the Army do. When they are called in to lay sandbags and rescue people - is that charged? Do the local govt work out which commercial company could do that and how much first?
The cost of a commercial outfit is known, because that is what they do and are set up to charge by the hour/day or whatever. But, it is my contention, the Govt is going to tell the MoD to NOT charge the cost to anyone. So you cannot work out the cost.
Lastly, I think that many tax payers would rather the Army do this than a commercial outfit.