I just paid for a 64 bit version of Ardour in Windows ($45 U.S.). I have also downloaded Ardour for Raspbian. I am still evaluating the linux download, and I am not sure if I will be using Ardour in Windows, or on the Raspberry Pi 3B+, or both. Do I need to pay anything for the raspbian version? It was a free download from the repository (stretch?).
No, you don’t need pay for it.