[spottiness]

That's only "renting" and prices are not too far off in Miami based on your numbers (a place equivalent to yours in Miami I would say cost "maybe" a little less). How about food, clothe, transportation? Are those things also more than twice more expensive? No way. For example, you can live without a car in SF because public transportation there is decent. In Miami you need a car as you need your legs.

And I'm not even considering the benefits that a globalized world brings to "expensive" cities. In other words, if we assume that everything is 138% more expensive in SF then savings will also be 138% larger and, in the "equivalence equation", you have to factor in the purchasing power of San Franciscans in markets outside SF and Miami, otherwise you'd be saying something of the sorts of: To maintain your standard of living when you move to SF from Miami you need to make 138% more money (and by the way, you'll get a 20 days vacation in Spain for free).

[mahyarm]

To be honest, you can usually shop better in large cities than you can in small ones. Flights are cheaper, you have more specialized discount stores, the amount of competition is higher. Big box pricing is also fairly consistent country wide. You'll find 'levi signature' jeans for $10 on clearance in the Mountain View Target and in the Austin Target.