Since this is theatre I'm assuming you'll have some sort of program for audiences? If this is the case, devote a number of pages to advertising and then sell this space to local businesses. One of our customers just sold us a space in their school plays program. I can tell you from past experience, we'll never get a single sale from it, and this is the way most businesses feel. However, it makes it easier for you to hit up the businesses when you're actually asking them to sponsor something rather than just dolling out money. As businesses we're almost obligated to buy.
Good luck