May I suggest to you, if you are arriving in the morning or afternoon at Las Americas airport you may opt to take a taxi direct from the airport to Bayahibe. Travel time should be 2 to 2.5 hours and the cost should be around RD $1200 to $1500, approx. US $85 .
Your planned option of going from Las Americas to Santo Domingo will cost by taxi about RD $250 to $400 to Hotel, US $22.
Plan on US $75 to $125 a night at the Hispaniola Hotel ( average price? ) in Santo Domingo
A taxi from Hotel to Bus Station RD $50 to $100, US $6. Bus from Santo Domingo to La Romana RD $100 to $120, US $7, per person. Taxi from La Romana to Bayahibe about RD $200 to $400, US $22. Plan to use up about a morning or afternoon traveling from Santo Domingo to Bayahibe.
Note: The prices for transportation are reasonable estimates based upon my own travels and information obtained from the board using the DR1 search option. Enjoy your visit. Regards, PJT
Web link for Hispaniola information follows.
http://www.tripadvisor.com/Hotel_Rev..._Republic.html