My plan B retirement calls for a nest egg of 600,000 euros for a 2,000 euro monthly budget. I have done a lot of research on this and I am absolutely certain I could live pretty well on that amount in some of the more rural parts of Western Europe. It would require a number of things however, including 1) living in a new 600-800 sq. ft., low maintenance, paid for condo. 2) Drive a small, gas efficient car(or use public transportation when available) and 3) The biggie, nationalized healthcare with low monthly premiums and equally low co-pays.
I would hesitate to apply such a plan in the US for one reason and one reason only: Healthcare costs. Even when covered with Medicare the costs can be staggering. My MIL spends more than $400 a month on Medicare part B and D premiums, Medicare supplemental insurance, and drug co-pays. Add another $150 for LTC. And she is very healthy for a 65 years old!!!
42 y/o, married, retirement portfolio = 43 x annual expenses