Help: Speakers to fill Exceptionallly Large Room?

I'm trying to outfit a large coffeebar with a decent pair of speakers or monitors on a budget. The room is approximately 20 feet wide by 80 feet deep. My current plan is to place one speaker at the front of the space aiming at the bar and a second about half way through the space, again, aiming at the bar. Everything beyond the second speaker will be a "quiet" space for all intents and purposes.

Rules are that I cant use more than two speakers and they have to be wall mountable. I'd like the place to sound good, though I know it will be no acoustic dream, by far. Price range is probably $500-600, $1000 max. Should be relatively efficient, because I'll need some db's to fill the space. Any help appreciated. Thanks.