Too many variables. Everyone has different hair density, different levels of "safe zones" and age plays a big factor. BeHappy nails it.
Which is why so many (good) doctors will steer you to going conservative as much as possible. More so the younger you are.
Very generally... if your donor looks good 6-7K I think tends to be the safer average to plan on, everything else after that is gravy if your own personal situation can handle it. Body hair/beard hair could add to it, but certainly more expensive.