The invoice I have been given isn't that detailed but states a total of 1.74 hours chargeable time.
To me, this sounds entirely reasonable.
You mentioned that the airfield is 15 minutes flying time away. So it'll be at least 30 minutes by car. Commercial schools don't have taxi drivers on the payroll. The only people around at short notice are instructors. So two instructors hop in a car, one is dropped off at the airfield to recover the plane, the other drives straight back. Instructor #1 then ferries the aircraft home in 15 minutes. Total time for instructor #1 and #2 combined: 1.75 hours. Other costs that would be entirely justified IMHO: 15 flying minutes, plus 60 car minutes (or something like 5-10 liters of petrol), plus landing fees and such.