Only use WLAN for a tournament if you ban:
- Microwaves
- Light Bulbs
- 'Cell Phones
- Computers
- Radios
- A lot of other stuff I forgot to mention
If anyone tells you WLAN is good enough don't trust them with any electronics, EVER!
Also it doesn't matter which medium you use (e.g. radio, copper, fiber) as long as you are in the same network
Just get ethernet adapters (they're like 15€ over here), a dumb ethernet switch with at least 9 ports (dumb as in only electronic switching without logic to it) and a router that's not complete **** and you're good to go. If you want to save money you can go for 100 Mbit/s or "fast ethernet" components because the ethernet adapters are only 100 Mbit/s.
A setup like this would be somewhere around 185€ including ethernet adapters. I think that's a fair price to run locals.
If you wanna go all out you could get 8 raspberry pis with a usb soundcard that have a line in and set up a mumble server to allow voice chat with mixed game and voice audio.
If anyone needs advice on how to setup networking for locals feel free to contact me.