I agree with everything 78F350 said.
Problem i see is that you often get crap on Evilbay. Don't ask me why i know. I run a business that is specialized especially in Porsche electronics.
https://sportwagendoktor.de
So make shure that you get ecus and key fobs that work. Also make shure they are especially for your car. Means it must be from a car with exaclty the same engine and the model year. Everything else will get you in trouble. And make shure you can return everything if it doesn't work.
The other route will be a used good M535 and new keyfobs that are programmed to the car. I offer these things, but i'm located in Germany, so this will not make sense for you.