Learned this the hard way. My rough math is this for SF:

1.5xCurrent Salary -- Because everything is expensive here

+ $10k / marginal tax rate -- for relocation and flights home

+ 500/month forEach dependent spouse -- Medical Dental Vision

+ 250/month for each child dependent -- Medical Dental Vision

+ X -- to replace spouses's Salary because they cant work

+ Y / marginal tax rate -- spending money to keep spouse sane because they cant work and cant stay home all day doing nothing

Edits: small clarifications, gross Y up by tax rate