They're a standard profile that any rubber specialist or the likes of Car Builder Solutions should be able to supply by the metre. You can also use a Mercedes Sprinter sliding door seal or something similar from the scrapyard.
It really doesn't need to cost more than a few £/m; what you get from Saab specialists is the same generic profile that rubber suppliers sell. I think I paid €35 for two cars' worth (so four doors in total) a few years ago, can't remember the length needed per door/ car.