For a room that size, with your budget, I would consider PA/DJ speakers. JBL, Peavy ect. These speakers are relatively cheap. They play very loud, and don't use huge amounts of amplifier power.
A standard mixing board can accept connections from your Blu-ray and such. But you will also have the options on a microphone, plugging in a guitar ect.
This could be very helpful for wedding receptions ect.
I would consider 2 main speakers at your "stage" then smaller speakers along the walls. Point the towards the back of the room, away from the stage. You will be able to control their individual volumes with the mixing board.
I think you goal should be to fill the room with sound, not volume. People love to hear music but don't want to scream over it. You will still have plenty of potential to really crank it up if you want.
I'm not sure but I think there is a DJ/Professional sound forum here, isn't there?