That's a really big room, if it were much smaller, I'd suggest one of the cheaper systems, but you'd kill it in that kind of space. Save your money up and go with something nice.
I've had about 6 total systems, my first was a ht-in-a-box deal, it was nice, but then again, my room is just 12x11. Since then, I've probably blown about $20,000 on gear, but I'm a nerd, so I'm allowed to do that.
Find a HT shop in your area, they can help you with almost any budget. Save up about $1500 to 2000 and you'll be able to get something rather nice.
I have a Definitive Technologies ProCinema 100 setup right now, but they suck for music, so my new system will be as follows:
B&W CM 4s for main l/r
B&W CM 2s for surrounds
B&W CMC Center
SVS sub (not sure which model yet... I may get two)
The rest of the equipment I already own...
Toshiba 40H80 16:9 hdtv
Yamaha HTR5280 receiver
Panasonic DVDRP91N DVD/DVD-Audio player.
I really want to open up my room, but I need to get a contractor in here to see if it's possible, the house was built in 1914, and every wall is probably a load-wall. Maybe I can get trusses or something. Or maybe I've been watching too much This Old House. :)