You would be able to get it done at any of the 3 main hospitals here. The costs would depend on the part of the body, so you would need to contact each hospital and ask for a price. They all have state-of-the-art equipment. Send an email in English to the email addresses shown on the Contact pages of the websites below.

http://www.centromedicodelasamericas.com.mx/servicios_Resonancia.htm

http://www.starmedica.com/default.asp?seccion=433

http://www.clinicademerida.com.mx/resonancia_magnetica.php