The buttons were used in anger today. A bit Heath-Robinson in appearance but they worked really well, despite my somewhat Prosecco'd colleagues pounding on them. Even better is that I got espeak to state the names of each group as the button tone
The final tweaks were to run the buttons with a daemon so they power on and are good to go. Just need to configure each of them at set up with a suitable name (I used REDBUTTON, BLUEBUTTON etc.
The controller (quizmaster) shows me which buttons are pressed and in what order. I should wrap that in a GUI with pygame at some point.
Total cost per button is:
Big red/yellow/green/blue button: £10
Pi zero W: £9
SD card, power supply etc. £10 (approx)
prototype board for Pi Zero: £5
NPN transistor for LED switching 30p
Casing/laser cutting/glue £4
so about £40 per button (unless you can get stuff at a discount)
For the controller I used a Pi 3 with a 7" touch screen and a couple of light up arcade buttons and a second WiFi dongle. Around £120 all in. However, all this kit is reusable for other purposes (and will be as I use the Pi Zero for teaching anyhow).
An easy project and one that is extensible.