Just as an added bit of information; if you have an emergency and have no enrolment in the IMSS or ISSSTE instead of going to a 100 percent private hospital for service you can go to the "Other Govt Hospitals (not clinics)" on the above list and the service will be fees established for INSABI as long as you are legally in Mexico which in my guess, depending on what services you require, will cost less than 1/3 the cost of most middle of the road private hospitals. Many services INSABI covers for free but not the more severe illnesses.
Another alternative is Star Medica which is a discount private hospital group - Carlos Slim is/was a large investor when they first started to open up, but I don't know if he still is - and get about 40 to 45 percent off what other middle of the road private hospitals might charge.