Re:
There's a section for price advice but I'll chip in. Ive had a few sets of the brakes and white industries hubs and the rock shox fronts too. Could do with them now tbh but hey ho.
They aren't that hard to come by, and prices vary from ones on ebay for years at unrealistic prices to more realistic. I've paid very little in the past for new or used versions, £30 or less) They aren't a great brake but are period correct and sometimes the only brake that will fit some frames and forks. Spares aren't easy to get either which is ultimately why I sold the sets I had.
Ultimately depends on your philosophy. Make someone happy and sell at a reasonable price, or hold out for more.
I've not seen one with the long arm before, I would say that is pretty rare but no idea if that makes it expensive.
