I've lived in both (Yungay and time in Maipú), looked at buying in 2019 Yungay/Ñuñoa (before October 18), and wives family is there, living in Maipú, Lastarria, etc... it's all kind of apples to orange though because the working class/middle class/upper class profiles are different than in SF. Maipú is probably the cheapest but of course you end up far away (unless you work in one of the places nearby, which is probably lower middle class to be honest).

Comparing via square footage, it's true - cheapest SF place is more expensive than most expensive Santiago place, but 3BR Parque Forestral penthouses (Even Barrio Italia) used to push $750k, for example, which you could get a 1BR place in SF for at the time probably too. If you go outside of SF city limits it gets much harder to compare.

Of course, these are just housing costs. Other things end up being more expensive in Chile in a different ways. We have kids, and even mediocre public schools like you find in the bay area are better than almost all private schools in Chile.