Nuestro Anniversario

So, I know somewhere in here I've posted that Michael and I are planning a trip to Mexico for our anniversary in January. We've even got the dates. The problem? Where do we go (that is, without breaking the bank). We originally thought Cancun, but we know we'd like to go down to the Playa del Carmen to go to one of their big sea parks. We also have an interest in going to see the ruins in Tulum or at Chichen Itza. So, then we thought, do we still want to stay in Cancun? Or should we try the Riviera Maya or even Tulum? I'm unsure and overwhelmed. I look at stuff online and there are lots of nice choices, but Michael's thinking more like an all inclusive thing for a little less than I was thinking we would spend (of course, typical male-female relationship.....I think). So...any deals out there that any of you know about? Please post a comment if you have any suggestions!