Eagle Crossbow
Brigadine Plated
eagle can go for like 40m and brigadine like 25m
Its a place to start, same as asking here. That thread represents the community's collective opinion, and it provides a generally agreed upon price for all the legendary items. Naturally the prices will fluctuate, but nothing too radical.
I would think that many opinions would be better than the one or two you may get from a WTK thread.
I would say Eagle is about 35 - 40 and Brigadine is around 20 - 25.