audio triggering question

Hi All,

I'm not sure this is the right place, but some of you might have an idea. I need to trigger the audio of a art exhibit when people either cross an electric eye or stand on a matt. The exhibit will be shown for a month, and the sound will drive the people working nearby nuts if it is left on the intire time. Any suggestions. We have a small budget, so ideas over 150$ are out of the question. Any ideas, suggestions, or links?