Thanks but my question is do I just show them my FM3 at the Juarez airport or do I need anything else? Also how much Mexican money can I have with me?If you will be coming back to Mexico when your FM3s need to be renewed, just get them stamped on the 'Salida' page.
If you have no intention of renewing them at the required time, in Mexico, you must have them cancelled by INM. If you don't, and you should return, you can be fined for every day that they were not renewed.
So, it is probably wise to have them cancelled and, if you return for a visit, use an FMT tourist permit.