Prius is a very good vehicle in terms of fuel efficiency but buying an old model can be troublesome, specially if the batteries are not in good shape, the new model would be very expensive to buy at first place.
I do not think that fuel quality would be such great issue in Islamabad has high octane is available and people successfully use it by mixing with normal fuel. Things like spare parts, finding qualified mechanic to work on it should something goes wrong and resale (if that is a concern) do not favor it though.