This is more of a home theater forum guys, you may be better off posting in forums that focus more on concert/band equipment. But with that i will try and help as best as i can.
This forum is for people who are typically filling small to medium sized house rooms with quality sound; loudness usually takes a back seat to quality as the rooms are small (compared to a hall banquet hall) and most speakers will typically be output plent of sound for our sized rooms. This is not the case for you. But a simple rule of thumb that most people base their speaker decision on is as fallows:
First decide how much power or room filling sound you require, you need ALOT; alot alot because your trying to fill very large rooms with sound (try calculating your average square foot of your venues, this will help you estimate what you will need for sound level output), then once you figure out that buy the highest quality sounding speakers you can, that meet your sound level requirements, and budget requirements. Seems obvious but thats what you will need to follow.
Danley Sound offers whats called the Labs DTS-10 kit, its an incredibly powerful well performing subwoofer more designed for concert type equipment. they send you all the prefabbed peices to build the box (enclosure) and the drivers/subs. You build it and save alot, and you get ALOT in return. Then you would rely on rack amps to power it all. this can be had for under $1000 and take care of ALL of your your low end bass. Call them they will help, and trust me its very easy to build, dont be discouraged, it has directions. Best value here. heres what the specs and kit look like:http://www.data-bass.com/data?page=system&id=4
as for speakers I do not know enough about concert equipment to make recommendations, but i would say try to score a deal at guitar center or craigslist for some nice stuff on the cheap. Its okay to buy used, nothing wrong with that, and for self starters like yourselves, you can save alot of cash, get BETTER equipment, and do larger events which means more $$$! My $.02.
Power: you will likely need rack amps on a portable tower (roller tower) to power all speakers. Amps DEF buy used, (again guitar center, Craigslist) they are typically pretty rugged, and you can save you boat load of cash.
For efficiency please do take note of the speakers sensitivity rating, This will be how efficient the speakers are at converting raw power into sound energy. The more efficient the more you will save on needing powerful amps to get the same amount of sound. try to shoot for somewhere between 92-100db @ 1watt @ 1 meter, less and youll spend alot on amps to get the same volume, any more youll spend alot on speakers which is not ideal for you case. i believe 3db is noticeably louder. every 6db will translate into the audience perceiving the sound to be twice as loud.
Make sure you match the amps to the speakers properly with not only wattage or power output but also by there impedance or load- 6ohm 8ohm ect.
Finally my last piece of advice, if your on a budget, it may be wise to get full range loud speakers. These as you are probably aware, these speakers output bass aswell as midrange and high end. Typically require amps. At your budget constraints, with the amount of sound you will require, this will more than likely be your best option.
Again i cannot recommend anything because i have not done enough research for these types of (concert)speakers to offer an opinion/ recommendation.
I hope this helps with my limited knowledge, but i think your barking up the wrong tree here. Im sure there will be plenty of members that can make recommendations aside for myself, but i think more could be had elsewhere in different forums for bands/DJ & concert equipment.