Even one of my favorites, Isla Mujeres (which I still love!) is getting too busy and full of annoyingly bad and overpriced touristy restaurants. Holbox is about to fill that slot. Holbox does indeed cater to tourists so you have a lot of fun bars and restaurants, but it doesn't have that "tourist crazy hype feel" ... yet.
Holbox, also famous for swimming with whale sharks (amazingly cool if you haven't done this already!), has the clear turquoise water, lazy sandy streets, chilled out feel you've been looking for. Go on a budget or fancy it up in a nice resort, you'll quickly be thinking like Brigham Young "this is the place". Oops, sorry for the Mormon reference, I used to live in Park City. ;)
It's a bit harder to get there than say, to Isla Mujeres or Playa del Carmen, but it's pretty easy in the whole scheme of things. Take the ADO bus about 3+ hours North from Cancun, then a ferry out of Chiquila, a golf-cart taxi into town, and you're in your new paradise. Very few cars, lots of hammocks and cold drinks.
Budget Accommodation
There are a lot of places to stay, but here are some that I bookmarked for my next stay:Omkar Residence Studio Apartment
Starting at $26/night or $555/month for a studio with kitchenette and not too far from the beach.Casa Vainilla Holbox Island
Bright rooms close to the beach with mini-fridge and balcony.La Casa del Pescador Holbox
Nice little hotel room with ktichenette.Casa Los Abuelos
Rooms with A/C and kitchenette.Room w/ Pool, 1 block from the beach
As low as $25/night for a room only a block from the beach with a small swimming pool.Hostels, Cabañas and Camping on Booking.com
Here's a link for other cheap places to stay on Isla Holbox.Booking.com