WebSocket Hub for 100 ESP32s

I have roughly one hundred ESP32 boards on the same LAN. A single Raspberry Pi will sit in the middle, behaving as a master gateway: it exchanges messages with each ESP32 over the local router and holds one persistent WebSocket link to my remote web server... (Budget: ₹1500 - ₹12500 INR, Jobs: Arduino, Embedded Systems, Firmware Development, Linux, Node.js, Python, Raspberry Pi, Software Architecture)