smart move to consider getting a taxi all the way there. Although it is of course more expensive the bus.
price should be no more than 2500 really. But it cannot possibly be less than 2000. I'd offfer a driver 2500 and I would be annoyed if he didn't accept it. If he was adamant that he wouldn't accept 2500 I'd forget that particular driver and ask another driver.
commence negotiations BEFORE you get in the vehicle.
go to the departures deck at Mactan where they drop off previous passengers, and where there is a taxi rank.
the distance is only about 100km but it will take 2.5 - 3 hours. Be nice to your driver. If you want to stop on the way for a bite to eat or something, include him and pay for his meal.