My recommendation would be for a HK Audio LUCAS system; One bass bin with built in amplifiers, plus two small satellite speakers. All on wheels, and easy to transport. You can get various sizes from 350 to 2000 watts output; mine is 600 watts, and plenty for that size of room. Add a simple unpowered mixer (Behringer or similar)and away you go. German made, very robust and sounds fantastic when amplifying acoustic instruments. The powered mixer and speakers route is ok; I used to have this setup before I bought the HK. I wouldn't go back. HK are not cheap (you pay for the classy engineering, not the name)but they do come up used on ebay fairly regularly.
Tim from Bit on the Side