Just before Christmas I spent a week at the Grand Bliss Riviera Maya, which is part of the Grand Mayan resort and not an all inclusive. It is very close to one of the Iberostar all inclusive resorts; I could see the Iberostar from my suite, which was 1100 sq feet and had a plunge pool on the balcony. The cost of my vacation was a flight, some points that I exchanged from my interest in another property, plus ~$400 in expenses for the week. That included all meals, entertainment, food that I bought and prepared, drinks at the swim up bars
the airport shuttle (it was free going to the resort) and several tours, including Xcaret and an all day trip to Chichen Itza on a luxury coach. There were several guests from the Iberostar on the coach and at the end of the tour we drove into the Iberostar to drop them off. They all spoke highly of the Iberostar. I checked the Iberostar website, which quoted an all inclusive daily rate of $600 ($4200 for the December week just before Christmas). I would not have paid that. I presume you got a better deal at the Iberostar you stayed at.
Addendum: I just checked the Iberostar Hotel Paraiso, which is comparable accommodation to what I had. $2975 US for a week in January for one person.