Mexico changed many aspects of the immigration laws in the "teens." Some of this info will change, but is pretty much accurate as of June 2019.
If you want an overview of whether you should consider living in Mexico, I offer a consulting service. (Opens in a new window so you can keep reading).
The changes already in place were major. What used to be called an FM3 is now a Residente Temporal - No Inmigrante visa. At the moment, you MUST apply for your immigration visa at a consulate in the USA or Canada. After four years, you can apply for the permanent visa - Residente Permanente which gives you more rights and enables you to stay in Mexico without having to renew the visa, as the Temporal visa does.
You will get a sticker in your passport, but the actual visa is issued in Mexico. Your temporary travel permit is good for only 30 days from the day you cross the border. You must appear at the IMN office wherever you are planning to move and apply for whichever visa you choose for living in Mexico. Therefore, I recommend you get your information directly from the Mexican consulate closest to you for the most accurate instructions at that moment.
Yucalandia.com has continually updated and accurate information on the residency maze. I bow to their superior covering of this matter. I will get your there with my roadlogs and maps and trip-planning. They will tell you what you need to make the move. Meanwhile, the info below paints the broad strokes.
There is another subset of this visa, the Residente Temporal con permiso para trabajo, which enables you to work in Mexico after you get a federal tax ID (RFC). Things will go much more smoothly if you hire a competent immigration attorney in Mexico before you even get started on the visa process to make sure you follow all the rules. If you become a working Residente Temporal visa-holder, you will be required to legalize your car in Mexico or take the car out of Mexico for good. At the moment this does not seem to apply to non-working immigrants.
Under no circumstances should you get a tourist permit (180 day FMM permit) if you have applied for, or already have, a validated Residente Temporal or Residente Permanente visa.
If the one you had is expired, you have 55 days to get a new one. Something new is that you have to get a travel letter from INM before leaving Mexico. If you don't get that, you could lose your Residente status. This is onerous for drivers as it gives you a short number of days to get to the border, but I don't make the rules.
While you can get this permit on your own, I think it is worth it to pay your aforementioned immigration attorney to help you get it. Life used to be easier.
Thanks to Jose G., a thoughtful reader, these were the financial requirements in 2018.
Thanks for Greg G. for that info.
Another reader (Dennis J) contributed this. He got his resident visa from the Tucson, AZ consulate. Other consulates may ask for more, like your address in Mexico, letter in Spanish stating you are retired and wish to live in Mexico. The key is to ask before you show up.
The total costs for actually getting a Residente Temporal visa for a couple is around $400-$500 if you use a broker or lawyer. It could be more or a little less. Much more, you should look for another lawyer.
I know people who applied in Canada, drove their household goods to the border and imported them under their exemption. When they arrived at their new home, they presented themselves to the authorities and their immigration permit was made official. Now this does not seem right, but that is what they told me. Verify that this will be the case for you if you apply before leaving the USA or Canada.
My general advice below is valuable in the sense that you should take your time before applying for a visa to live in Mexico. For even more words of wisdom, consult with me one-on-one.
Don't rush into getting a Mexican visa. You don't need a Residente Temporal visa to live in Mexico. You should live as a tourist in Mexico on tourist permits (FMM - Forma Migratoria Multiple - good for 180 days) before making a decision. I recommend you live in Mexico for a year before you decide if living in Mexico is right for you.
Then you can decide whether you want to go through the bureaucratic maze necessary to obtain a more permanent visa.
You will find several different products relating to living, working or driving in Mexico on my shopping cart, as well as a description of my consultation services to help you decide if, and where to live in Mexico.
Your pet will also need papers (although my dog snorted and said, I don't need no stinking papers). 90% of the time, you will not be asked for your pet's (dog or cat) Mexican immigration papers. It's only a pet certificate of health issued by a vet, but my god, er dog, thinks they are immigration papers. Other pets are difficult to bring to Mexico.
If you decide that living in Mexico is for you, you will want to look into the requirements for a Residente Temporal, No Inmigrante visa or a Residente Permanente visa.
You do not need a lawyer to get your retirement visa, but since things are now so complicated, I recommend you find a GOOD immigration lawyer. In many areas of the country, particularly Guadalajara, the Gobernación officials speak English. If you are in the Guadalajara area, go to the Lake Chapala Society and you will find someone to help you if you need it. In San Miguel de Allende, you will always find a helpful soul.