if you assume a 4-5% return on the money, only want to live off the returns (not the principal) and "six figures" (say, $250,000) is enough as yearly, net income...the lowest a person would go is about USD$6.7MM (after tax, of course)
EDIT: On further thought, I'd go for much less, I think. It's really just a comparison the money offered against A) the amount I'd expect to earn in those 3 years, B) expected loss of lifetime income due to the time lost and/or resulting stigmas, and C) personal discomfort/inconvenience of the lockup time.
Hard to figure the latter two, but I expect even half a million would tip the balance in my case.