What do you mean "retire"? Can't you do that for free anytime you want?
he mean no more work, just an happy life
i would say 1M dollar at least
You can do that already for almost nothing if you have a couple friends. Just chill, you don't need 1M dollar to do nothing. But why would you want to do nothing anyway?
Oh I know, maybe by "work" you mean something that somebody else wants you to do but you don't really want to do so much yourself apart for some financial gain?