Hi Ian,
What would you consider quite expensive ?
Where i live these French daggers are very hard to find (in any condition, but especially the well preserved first generation versions like this one), so i just tend to follow the ancient Dutch proverb: "better expensive than not for sale at all".
Now i also want to find it's brother, the French Green Beret dagger (Poignard de Combat Berets Verts), which looks even more like the Fairbairn Sykes model, but just like my Red Beret dagger has a bit sturdier build quality compared to those, as well as a different sheath.
Pics from the net:



BTW: later versions of all these knives indeed had stainless blades afaik.
Mine not only had a patina on the blade but also patches of red rust on the tang under the brass handle (which is all gone now)
The main reason my Red Beret dagger looks like it was never used or even carried is the fact that it had only rudimentary edge bevels that weren't even apexed, and it also only had a narrow rounded section where originally a sharp point is supposed to be.
My guess is that it must have slipped the final quality control, or the worker just didn't care enough.
So i used my Tormek T7 wet sharpener and a special home made jig to create what looks like narrow factory bevels nicely coming together in a symmetric and needlesharp point, making it fully functional again while at the same time preserving that untouched appearance so it looks like nothing was done to the knife.
Anyway, i'm very pleased with the result myself.