Was looking to see if Mexicali were doing a valentine's deal to compete with Mad Mex & came across this, BOGO for their new Vegan Chorizo Tacos. It's effectively $7 for 2. Offer is valid to 8th March, can only be used once per day and up to 5 times in total per customer.
Although the default is vegan, you can add sour cream or cheese for free. But you don't seem to be able to customise each taco only both. (Their site doesn't seem to have the option to buy 1, they really want you to do the BOGO.)