I will second Isis for rentals though they don't have a airport location. What you will find is that the others advertise a really cheap base rate that doesn't include liability and CDW insurances, which will be from $25 to $40 per day just for the insurance. Isis rates include all insurance and if you're nice they will drop you off at the airport. If you're thinking of taking your chances and forgoing the CDW/liability insurances (which I always do in the states), do some research into the potential consequences.
Driving in Mexico is not for the faint of heart or the slow pokes. Many intersections have no lights or stop signs at all, you're supposed to just know who has the right of way. And drivers there have little patience with those who dally around indecisively. It helps to know some Spanish to read the signs, starting with the most important one, "Tope". It's not a sign you'll overlook twice!
