Well $300,000 dollars (3.78 million pesos) looks to be "safe enough" if I am doing my math right. But only if it is greater than 1.5 million pesos per person .
$500,000 in aggregate would be better, but it is the "per person" that needs to get up there. 1.5 million pesos ($118K US dollars) will blow through the $100K pp limits on the $300K policy sold online even before considering the PD.
I will be calling around. This is a manageable risk. Insure around it.
Edit: The online quote and buy page for mexadventure only has $300K per accident $100K per person
coverage which does not
cover the high wage earner scenario mikemike mentions. Additionally, it appears these policies are "combined limits" which apparently means that PD comes out of the same liability pot.
I have sent an email asking for a phone consult and will report.
For those interested, here's a link to another forum discussing the same thing.