Free of charge as part of any projector hire
Every Mac with a Mini DisplayPort allows you to connect an external display or projector using an adapter. You can use an external display as your main workspace or to extend your desktop, or you can work in mirrored mode with a projector so you can view what your audience sees.
Use the Mini DisplayPort to VGA Adapter to connect your Mac to a standard analogue monitor, projector, or LCD that uses a VGA connector or cable. Review the documentation or check with the manufacturer of your monitor to make sure you're choosing the right adapter.