Pre-Pay for Street Performance
A different way that might make more money (and sense.)
Put up a poster advertising that your show will start in X minutes – if enough money was deposited into a special box. The box shows how much money has been given, and when it’s close to the minimum target, it shows how much is still needed for the show to start. The poster should also advertise and “sell” the performance since that is the only base for payment the viewers have. A small screen with video highlights can also be used. The box should also stay open to donations during the show.