You can get something decent in that sound range...
Amazon.com: PEAVEY AUDIO PERFORMER PACKAGE INCLUDES MIXER, 2 SPEAKERS, 2 STANDS, & 2 MICS: Musical Instruments
http://www.amazon.com/Peavey-Escort-3000-7-Channel-Two-Way/dp/B00B8QC9O0/ref=sr_1_1?ie=UTF8&qid=1413119949&sr=8-1&keywords=peavey+escort
the escort systems are nice because they fold away in a neat little package, they have larger ones but the 3000 falls in your bidget, the performer package is what I would go with. You can always add active subwoofers later on if you want more bottom end punch...
If you dont need a mixer and mics, and you are just going to use an ipad or iphone ect for a source then you can just grab a pair of powered loud speakers and plug the source into them...
like a pair of these...
Amazon.com: BEHRINGER EUROLIVE B212D: Musical Instruments
I have spent much more on my "party system" and notice the only time we really crank it is when the kids are having a party, our parties have gotten much quieter over the years... We have something like this
Karaoke Laptop Karaoke Computer Karaoke System Professional Peavey Speakers Mics | eBay with dual 18" subs and 15" monitors powered by crown amplifiers, it turned into a pro setup from something I wanted to simply throw together, but we have used the karaoke functions many times, and if I add up what we saved not hiring DJ's then the system has made me money... Dj's around here get $550 for a 4 hour birthday party, we throw a lot of parties and entertain A LOT out side so it was worth the larger investment, granted I could do it all with a nice $600 setup, I talked myself into going a little further with it...
If I were you I would go with the performer package, peavey is great stuff, you can add a good amount of function to that setup, and them speakers will be WAY more than you would ever need inside a building, outside some low end sub support may help with bass heavy material but they should have no trouble projecting a 50ft dance floor...