A. Apple TV for $109
B. If your projector (and cables) are VGA, which is the most likely situation:
HDMI to VGA adaptor (MonoPrice or DealExtreme) or cable for about $40
VGA switch (MonoPrice) for about $15
B. If your projector has a DVI input:
HDMI to DVI adaptor or cable (MonoPrice) for about $5
Unfortunately DVI doesn't carry audio, so to get audio to your speakers you'll also need a toslink to stereo audio converter ($25) and an optical audio cable ($2), or something like this for about $45.
B. If your projector has an HDMI input:
You may need a long HDMI cable, or just a short HDMI cable. You can often even get these at the dollar store.
C. Computer speakers (preferably with two audio inputs, at least 10 W or so) $30 to $60.
Unless you already have some speakers you can use, or if your projector's built-in speakers are loud enough.
A few other notes:
- Apple TVs can now be connected to the XXXschoolguest networks in schools, see this blog post for AirPlay details.
- Set the Apple TV to projector resolution, probably 1024x768 (Settings, Audio & Video, TV Resolution)
- If the image is purple tinted (or some other color), set the color space to RGB (Settings, Audio & Video)
video on how to mirror your screen using AirPlay