HDMI on a receiver does absolutely nothing for you in terms of quality improvement, outside of obtaining lossless audio from either BluRay or HD-DVD. Even if you were obtaining lossless, you are still better of spending first where electrical energy is converted to mechanical energy: the speakers and sub.
So, that being said, if I was only limited to HTIB, modest budget, and had to have all pieces at once, I would look at the Onkyo THX 990 being had for $700 or less.
You can be guaranteed that others will chime in and just convince you to build pieces at a time, ie receiver + pair of speakers, then sub, etc...