Have you entered them into any shows? Before I priced them I would have proof that they were bred to standard. I know the APA has not sanctioned the silver lacing variety, but judges will still give you best in breed ,if your birds are closer to the standards then the others Brahmas.
A good example for people interested in showing, is the BLRW in the US. While many of the breeders have done a phenomenal job getting the lacing down, they birds , when put up against show stock wyandottes, will get clobbered. The backs are to long , chest to flat , butt to narrow, etc. When developing to a variety , you must make sure you match the breed standard.
I think sir you are to be congratulated on your endeavor , you have produced a beautiful bird, that apparently will reproduce itself, all offspring will have the same basic characteristics, an incredible feat, something I would never have the patience for.