It reads like the current system is probably using AX.25 wireless packet radio to communicate with the other schools. I suspect this type of use case with amateur radio is, at best, a grey area in terms of regulatory compliance. The replacement still shouldn't cost as much, but I'll bet it's more than just replacing the PC. It's also coming up with some kind of cross-school network, if one doesn't already exist. And compliance with the inevitable mountain of government requirements.
Another comment mentioned this already, but a single low end PLC for the central control unit (such as https://www.automationdirect.com/adc/overview/catalog/progra... ) plus RDCs at each building would cost under $5000 easily, all while being in compliance with any standards governing such equipment.
