That's the thing. An agency has a flying budget. The pilot, the TT straps, the phase inspections etc. are already paid for. Rotables that come due in the next budget year get put in the budget. An agency doesn"t put money in the piggy bank to save up for a gearbox overhaul. They just pay for it. The cost to operate a snowplow, helicopter, sewage pump 'one more hour' is limited to fuel and oil. Fuel is bought in bulk, probably through one of the fuel card vendors, so the cost to the state is not what it would be for someone who just tells the fueler 'fill er up'.
So while it would cost a commercial operator $550/hr to operate a Jetranger (and $950/hr to charter), it is entirely possible that the 'cost' in agency internal accounting (e.g. If agriculture needs to use fish and wildlifes helicopter) is indeed $250/hr (and that's how we end up with trillions of public debt ;-) ).