I believe the taxi rates are posted on the Punta Cana forum. Search for taxi rates and you should find what you need. The majority of hotels have a flat rate. I believe Iberostar is about $40.
I arranged a shuttle service for 5 people (90$ round trip). A friend took a cab from the hotel to the airport and was charged 40$
We took a shuttle that was arranged through Apple Tours. I believe the cost was $15.00 per person each way.
We had a private taxi booked through our travel agent. It's us £80 return
We had a private taxi organised by our travel company. We paid $70 for a return trip.
Get an answer from Iberostar Grand Bavaro staff and past guests.