While I have my own mikes and a couple of monitor speakers, owning a sound system capable of playing to 300 - 500 people outside is very, very expensive. The speakers alone would have been an addiitonal $1400, easy.
Instead, I found that Guitar Works has great renatl sound systems for under $100 featuring Yorkville speakers and powered mixers.
The staff was very helpful in showing me how to hook everything up and managing it on the gig.
They are real pros there.