POE-Powered RS485 Sensor PCB

I need a compact, production-ready PCB that lets me power a 12 V DC / 200 mA RS-485 sensor directly from a PoE network drop and expose its data on the same Ethernet line. The finished board must fit inside... (Budget: $10 - $30 USD, Jobs: Circuit Design, Electrical Engineering, Electronics, Embedded Systems, PCB Layout)