With a $500 budget- you would have to find some really cheap speakers and assume the labor would be free.
You just really don't have much money to work with.
Well, the labor would be free, and I don't think $500 is a hard number at all. That was just out of my head in thinking of trying to think about what we might be ready to spend for a single speaker without even asking the board etc. A better system could probably be "sold" to the decision makers if we knew it was going to be a good long term solution.