I would not trust a site (travel club) offering rates this low. It's probably a scam..

Trust in airbnb and rent from a local property owner, if you don't know the market and want a smart place to stay. Or look at reviews for local hotels and contact them directly. Book flights with airlines, do it all yourself, and you will have a great time! ;-)

Reputable vacation-rental sites are: HomeAway, FlipKey, or Airbnb, all of which will protect your money from fraudsters.

Bali is very nice; I never found diving like Cozumel. Bali has colorful fish and mostly dead coral, in my experience. Maybe I don't know the right place to dive.. I don't recall where I was exactly.

Cozumel has the best diving toward the southwest of the island. I would recommend Cozumel if you want to see the most colorful coral reefs.

I put a little more in this post on Cozumel diving:

https://steemit.com/travel/@surfyogi/ultimate-travel-scuba-diving-in-cozumel