Historically, the weapon of choice in reaching analog shutoff (ASO) goals set alongside digital terrestrial (DTT) programming launches has been the digital transport adapter - a relatively low cost ($20-$40) box that receives digital signals and converts it to an analog format (Coaxial or composite video) to deliver to an existing TV.
Advanced Television reports that Mexico will instead deliver 21 inch TVs to 13.8 million low income houses. The cost per TV (presumably including administrative and delivery costs) is said to be US$105, an appropriate level for 21 inch sets (which you can buy today at Walmart for $120-$130). Mexico's plan likely has a few side benefits, including that LCD TVs will have much lower energy consumption than the legacy sets that they are replacing.
Nice move - and one that will no doubt catch on in other countries.