Sorry no one got back to you on your query regarding Costa Maya so I'll throw in my 2 cents worth.
First of all, what do you like to do--are you interested in Mayan history and Mayan ruins? Would you rather just spend time on the beach , shop, etc?
I've been to Costa Maya three times and like the port. It's located on the mainland of Mexico and not an island. Some folks don't like it, says it's a " fabricated , or man made port / shopping center" but in reality, so's a lot of others.
If you like Mayan ruins and sites, there's some pretty interesting ones to see but they will require a pretty fair amount of your time to get to and from them. There's a shopping complex right at the pier that has some nice shops, a couple of restaurants, bars, etc. and a swimming pool right in the middle of the complex. You can find most anything you're looking for at the shopping complex--don't remember seeing any big name jewelry shops there but that's something I would ignore anyway as my wife's in the jewelry business.
There's a small village down the coast about a couple of miles --Majahaul
( spl? ) that has plenty of small shops, bars, beach area, massages right on the beach, etc. all at very reasonable prices.
You can catch a cab from the shopping complex to Mahajual or get a bus. The ticket / cab area is around behind the complex--anyone can show you and there's signs too--it's not a big area anyway. I was there back in Jan. and If I remember the bus ticket was something like $ 2.00 per person one way.
This area was basically wiped off the earth by a hurricane 2-3 years ago and was closed for quite some time as a port-of-call for cruiseships. But, it's back now and doing well.
I would advise that if you want to see some of the Mayan ruins to take a ships tour as they're pretty far out. If you were on your own and a problem developed , you could be left behind.
If you're interested in just relaxing, shopping, etc. I would suggest you go first to Mahajual ( you can see it down the coast from the pier ) via a cab or the bus. Spend whatever amount of time you want to there--relaxing on the beach, getting a massage, having a drink, shopping, etc. and when you're ready to return to the port complex, there's cabs aplenty to take you back.
As I said, I've been there 3 times and will be going again in Feb. so I like it. It's a relaxing stop to me. If you're looking for another St. Thomas type port with a Jewelry store every 10 feet, then you may not like Costa Maya but for something different it may be your cup of tea.
I hope you enjoy your cruise and hope you find something interesting in Costa Maya.