DC area *is* slightly more pricy than many when you consider flight, lodging, and food, but I also thought it was one of my favorite places to visit when I had no money, just because all the sightseeing is cheap or free. It is probably the friendliest location to young (<21) folks because there's lots of stuff to do.
Vegas is cheap for flights and lodging, but can be down right hostile if you're young, and I've found that in recent years entertainment costs have gone nuts. Still, as a central-ish location that is easy for everyone to get to, it works.
But the thing that really makes a key con awesome is when someone, or a team of people, who are willing to do the heavy lifting of playing host. With that in mind, it's going to be tough to beat XMIT's offer of Austin. While most people think of the cost of attending, the quality of the event is all about planning and ownership. Having events, demos, and a big collection already ready to go (my fave part of the CA con was the crazy historical collections gathered in one place), Austin is probably the best plan at this point.