Most of the times eating out is not my first choice when I travel, and that was particularly true in the Yucatán Peninsula, where I spent 5 weeks.
From what I experienced I have to say that veganism is not widespread and typical dishes are mostly made of (or with) animal products; even if you want to eat something apparently vegan like rice with beans you may discover that they may contain lard.
There are two cheap things that you can find without going to a legit (and maybe expensive) vegan restaurant, and they are rice with vegetables and guacamole, and tacos with vegetables and guacamole… I really enjoyed them the first times, but I have to admit I got fed up quite soon and I really appreciated having booked accommodations with a kitchen.
Even if I was traveling on a budget I decided that I wanted to try some of the vegan restaurants suggested on happy cow, and here’s my experience:
Eating vegan in Cobá
Cobá is a really small village close to Tulum and it's really worth a visit for its archeologal site and, most of, for the natural reserve of Punta Laguna.
I spend 3 days there and this time my accommodation didn't have a kitchen, so I had dinner at the restaurant Chile Picante; thay have vegetarian dishes on the menu which are easily vaganizable, the staff is really friendly about that.
Eating vegan in Tulum
I found this place extremely comfortable and well decorated, their choice of vegan food is huge: you have sandwiches, bowls, natural juices, sweets... Prices are european, I remember I spent 120 pesos (6 euros) for a vegan hot dog.
They also have a natural shop inside where you can buy food and household products.