Volaris is a great value but their website appears to have been designed in the 1990s, and certain practices are probably not legal in the US.
The first point, the website is painfully slow and tedious. To top it off, for whatever reason, it defaults the US to pricing in Mexican Pesos so unless you are aware of this and manually change it, you may be deep into pricing you may have to start over to get your fare in dollars.
Further, as you go through the search process, certain windows (like the calendar window) will pop up then suddenly shift up a few lines ..... causing you to hit the wrong date and thus probably forcing you to start over.
Finally, when booking their flights, it opts you in for both their Trip Cancellation package ... forcing you to return to manually remove it, and it also opts you in to pay approx. $7 per specific seat reservation, again, forcing you to return to manually remove it.
This is probably because it's aimed at less internet savvy Mexican travellers who just pay what the final price instead of questioning why they're not getting what was advertised. These deceptive practices are probably a legal issue in the US but not in Mexico.