Seems very weird imho...
I'm sorry dude but there seems something off here. That's a hell of a lot of money, and yeah, your relationship will never be the same again (you reckon once will really be enough for her?). Also, (and sorry to be a downer here) but have you considered possible ulterior motives? (eg she wants to get pregnant, get revenge on some ex, or turn around and charge you with rape?) It's probably unlikely but you can't be too careful, people can be disturbingly duplicitous. And speaking of disturbed, how's her mental health? Cos if she's say BiPolar or has a Borderline Personality Disorder then going through with this is likely to cause you some MAJOR dramas later on...
But hey, yr a guy right? Chances are it's already too late, right? lol