yeah, that diamond you're looking at is overpriced.
just finished my ring purchase last week (picking up the completed product today, in fact).
i ended up with a 0.620 VS2 G, ideal cut, with a HCA score of 1 and excellent in all four categories. the ring is a custom job that my local jeweler made for me (kind of a torsion mount half bezel wraparound).
the ring appraised at just over $3000 - i paid $2000 for everything.
BTW, dirtcheapdiamonds is where i picked up my stone. blue nile had the same stones, but they were more expensive, often by several hundred dollars.
good luck - it sounds like you've done your research, but don't get hung up on that seemingly all-important carat weight. get a stone that's cut properly and it will look bigger than it actually is almost all the time.
/popping the question next week