I don't think that budget is very reasonable for such a project. Have you priced ethernet magnetics? The major development expense will be in the firmware and the time it will take you to either learn a packaged library and adapt it or write your own ethernet stack from scratch.This is a project with a strict $18 budget for mass production. The PoE is Power over Ethernet and I will be using a module as it was cheaper then producing one myself. The MCU will need to be atleast 16bit for the calculations that will be done along with a 12bit ADC is now prefer for accuracy. I am looking a a PIC24F or H with a ethernet controller SPI.