I'll take T-Al's and calmloki's approach. I think back to key times in life and what "millionaire" meant at the time. Assuming 3% annual inflation (which is not entirely accurate, I'm sure, but it'll do) here are my key years:
1959 - $ 4.01 M (birth year)
1969 - $ 3.07 M
1977 - $ 2.43 M (HS graduation)
1981 - $ 2.16 M (college graduation)
Why is 1969 important you ask? Peak viewing period of Gilligan's Island reruns and identifying Thurston Howell III (the "millionaire") as really wealthy.
So I voted for $3M.