I have used VivaAerobus since they started operations in Mexico like a year ago, they are very cheap but you have to expect what you pay in price. You don’t get a seat assigned, you have to make lines, first to arrive are the first to get in to the plane and choose their seats. The people with children, handicapped and pregnant ladies are also on the first line...
They sell the food and drink: sodas, beer, chips, sandwiches, etc. The seats do not move, so if you plan to sleep try to get a window seat so you can place your head against the wall or window.
Also they are not too good with the timing; they are between 75-85% on time. So please be careful if you have connections because they are a charter company and they won't be responsible to put you in a different flight if you miss yours because of their delay.
The planes are old, but with all this said is really good to have a round flight of $50 USD if you buy them on the special offer. We got those and we are going to do a second site visit LOL next week to PV...
I have used them for Cancun, Puerto Vallarta, Hermosillo and Merida and I haven’t paid more than $120 round trip for any of them..
So if you don’t have issues flying cheap... VivaAerobus is a good choice.