I also have a very large room (26 x 16 x 8). Across the front I utilize the HSU CCB-8 which is a concentric bookshelf speaker (tweeter imbedded into an 8" woofer). I also run a Buckeye Hypex NCx500 class D amp across the front stage, 2 SVS 3000 sealed woofers, Kef Q150's as the rear surrounds, and an SVS Ultra Surround as the back surround.
Goven your price range, The CCB-8's only run around $400 each and they deliver great detail and offer a very nice soundstage. The bass goes down to around 50 Hz. In my setup, (7,2.2) these sound very good and help fill my large room with sound. I run dual subs which help a lot, and the Buckeye Amp was a recent addition; it brings out a lot of additional dynamics across the front stage.
Good luck in your quest for a relatively inexpensive bookshelf speaker for a large room.