Reply to Speakers for a gig outside??

Hi! I have a gig coming up (about 50-75 people)... It's at someones house in their backyard and it's quite big. My small M-Audio AV40's aren't going to do the trick although I may bring 1 as a booth speaker... What I need to know is what speakers I need to buy for the gig. I would like to keep the quality of the speaker decent and loud without spending a ton of money. It would be great if anyone could recommend a brand and model of speakers/sub(is a subwoofer necessary?) Thanks for the help!

~MIDI Powers