What all turistas need to have in México is not only liability insurance but personal medical coverage, should you be taken to a hospital, clinica, Cruz Roja (Red Cross) or the local shaman, your insurance should be able to cover your medical expenses not just the other person and every one in your vehicle, the other item de rigour is immediate access to a lawyer, in México you are detained if you can not or do not have enough cash, or insurance coverage, you are held in custody even if you are a witness and much more so if you are involved, even if it is not your fault!
That is why you need immediate access to the lawyer.
Get coverage for liability and full coverage for everything else, being detained in any Mexican jail, not arrested just detained is no fun at all, until they investigate whose at fault and that can take several days, that is where the lawyer comes in handy.
Trying to save some bucks is not worth the agravation and anguish of being taken to the comandancia,
I have found that a full years cover is cheaper than only a half year.
navegator