For a senior developer in SF area, 3 months salary could get you a loose diamond in the 3-4 carat range off a site like bluenile.com. That's enormous for a ring. In fact, probably so large that disbelief becomes a problem: "That can't be real!"
Wowsers. 1.5 carat solitaire rings look quite huge, 3 carats would be enormous.
I'd be kinda tempted buying one that big for a woman because, you know, if we're going to go for a vulgar display of wealth, then let's make it really f*cking vulgar :)
(I still have better things to do with the money...)