I really like the idea behind the Propeller Aeropoints. Those are basically GCP targets with integrated PPK GPS. They are quite expensive, about $6.000 USD for 10 pieces, but that's still cheaper than a professional surveyor-grade RTK system, and probably more convenient for UAV mapping purposes.
However, I was wondering if a DIY version is possible and pays off?
In the end it's just a PPK receiver with power supply sitting in a rugged plastic plate... can't be that expensive...?