As far as the ring goes, I'm not a fan of arbitrarily spending 2 months' salary on a single diamond and then having it set in a generic band. You've known the chick for a while, you must have some sense of her style, so why not look for something unique?
When I got engaged, I had a jewelry designer buy 5 smaller diamonds and have them set in a unique band. Not a difficult process, and not much more expensive than buying a run-of-the-mill solitaire in a gold band. Sure, she got a few comments like "that doesn't look like an engagement ring," but neither of us gave a crap what anyone else thought.
Of course, we're not together anymore, but that has nothing to do with the ring
As for your future father in law, if you do it that weekend he'll have two things to be happy about.
