You don't necessarily need one GPU per person. You can do just fine with just a few GPUs
You can run a program called "SoftXpand" to create different workstations for multiple people.
This build will run CS:GO across the 7 people at 100fps each.
https://pcpartpicker.com/user/baconbeef21/saved/#view=pndKHx
THIS INCLUDES THE MONITORS AS WELL
You can pick up a few keyboard/mice combos for $25, this CM STORM DEVASTATOR combos are pretty good quality, and will work for this build. In total, to have 7 PC gamers play at once, it costs approximately $3,500, almost 1/10 of the price of Linus's build.
With this build comes issues though. It is a pain in the butt to set this up