How much $ is needed to never have to work again?

[maxtower]

You could buy dividend paying stocks, such as the mergeant Dividend Achievers index. The growth rate of the dividends is faster than the rate of inflation. Principal will fluctuate, but you'll only be spending the dividends, so you won't have to actually sell any shares. This should insulate you from the big early drop scenario that destroys a lot of retirement plans.
Buy enough shares to pay your monthly expenses.