https://store.freeflysystems.com/products/rtk-gps-ground-sta...

Not cheap.

Theres also services like this: https://www.septentrio.com/en/learn-more/insights/gnss-corre... that offer correction information.

I expect starlink to eat that industry shortly. Not sure how they'll make the strategic steps though. Mandatory location data for cell phones to talk with star-link? Wait for whatever satellite septentrio uses to EOL and offer a deal to use star-link instead?