You're refuting a point I did not make.

I was responding to someone who suggested that schools should build their own critical software. If there's a good FOSS option already, they should absolutely use it. But there isn't always that option.

Also, I guarantee that the school has at least 5-10 tech people, which means computing expenses are approaching $1M when you factor in benefits. Free software requires a larger in-house staff to customize and maintain it, even if the initial cost is low.