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.
There's a used pair of Bose 901's that were just posted. These are great for bouncing sound around and filling up a space.
Look for a pair of of used OHM Walsh 4s or 5s if you can find a pair local to pick up. They are big and heavy and tricky to ship safely. You probably want an amp that puts out at lest 80-100 watts or so though to really get them going.

Smaller and easier to handle Walsh 2s might cut it as well. I had a pair once running full steam outside on a farmhouse porch off an 80 watt/ch Tandberg receiver and it sounded like a live band playing a good 80 yards away of the best "home audio" sound experiences I've ever had.
Pro series, wall/ceiling mount line arrays from Toa fit your budget. Also, look at BG Radia. Both almost require a sub, like all wall mounts.
I second the Bose 901s. You can hang them from the ceiling with chains and they are efficient and not demanding of the electronics that drive them. They have always worked great in bars and the like.
Klipsch LaScalla
Klipsch La Scalla II
I can recommend Altec Model 19s. They are large, informal, decent-looking, very efficient, have a long "throw", are dynamic as all get-out, are only somewhat difficult to find, and have good resale value. They can be found in 'beat-up" condition (which will be in your budget) or absolutely mint (which probably won't be), and don't sound tremendously different either way, and can be "restored" from beat-up to OK-looking with a bit of wood-finishing (but one has to be sure the woofers/drivers are OK). They tend to roll off a bit in the treble, and they don't do 20Hz at the bottom end, but for a cafe, that's probably better in both cases.
Bose 901s efficient? News to me but they must have changed during the years. The originals were notorious for their INEFFICIENCY. No surprise as they were based on table radio speakers equalized so that their midrange was suppressed to the level of their treble and bass. Anyone familiar with the response curve of typical small single cone drivers will appreciate what is required to do this.
The Bose 901s hanging from the ceiling is a great idea as critical listening isn't going to happen in this setup anway. I had a pair hanging in a basement 20 years ago. They could fill the place with sound.

Beginning with the Series 3, the 901s could be driven to very high volumes with a good 75w/ch receiver. They do require use of an equalizer (included) that runs through a tape loop. Finding a modern receiver, integrated amp, or preamp with a tape loop could be challenging.
Pro stuff?
"they were based on table radio speakers equalized so that their midrange was suppressed to the level of their treble and bass. "

Didn't realize that. That is an innovative design! No wonder their sound was so unique and sought after by many!
Altec much better than Klipsch
Don't fool around, JBL Everest 66's. They are visually a statement. However, at $60K for the pair, you may need another loan.
A Fischer table radio to be exact. They had a famous law suit the went the the US Supreme Court over Consumers Report's description of their sound. A British mag commented that it was a good thing that they hadn't seen ITS report. I can't recall if it was the one that said they sounded as if the tenor had stuck his head in a barrel of cotton wadding. My totally obsolete data retrieval system [aging memory] now recalls that they switched to plastic framed drivers in the past. The first ones were at least well made, the later ones, well everyone to their own taste.
Get a pair of DJ type speakers.IMO,in a business atmosphere,people are not that interested in how the music sounds.While lots of the speakers recommended above would be fine,why spend that much money on more or less,background listening.Just a thought.Good luck with you business.Here's a link to a site with a good sale going on.