Thank you guys for all your answers!
The person who is going to fly this plane as a passenger is a frequent business traveler (max. 1000 km). Time is the key here. What we are trying to compare is: cost of an airline ticket in business class + lost time for transportation to the international airport (150 km from our place), waiting time and time of the flight VS. costs of doing the same route in own aircraft (taking into account whole operating costs + lease payment) + lost time for transportation to local airport (we have two here - 30 km to a bit bumpy grass airfield, 60 km to concrete runway) and time of the flight.
We already did some initial calculations. Unfortunately, because of the distance to the concrete runway (more lost time) we have to resign with jets. It turns out that the ideal candidate will be a plane worth around 500 000$ (might be a bit more), fast as hell (at least 400 km/h cruise speed) and able to take off from 800 m bumpy grass strip.
Thanks!