I haven't been there but I'm a friend of the internet.
Check out this website. http://www.huatulcokiosk.com/huatulco-tour/
There are 36 beaches near there and the weather is suppose to be amazing I have heard great things about Oaxaca and Huatulco (wa-TULE-co) is a developing resort area in Mexico, in the state of Oaxaca. Bahias de Huatulco National Park also sounds interesting, I love tropical plants. What cruise are you taking that has this as a port? I would love to see this place.