Late bump, so I have a feeling he ain't gonna see this, but what the hell...
First, did you ask the venue if they can crack off some dollars for promo? What's your relationship to the venue... it's unclear if you're 'volunteering' or you're the proprietor etc. Never solicit free work, least of all here, you got off pretty easy
Here's a little DIY tutorial that you might find useful:
Search "site:gutenberg.org" on Google Images. Those are works which have entered the public domain. Find a striking image (up to you if it has anything to do w/ the headliner / bands), crop it if the scene is too busy, and slap a bold headline + details. If you're going to print color, when in doubt less is more.