To address the original post, prices are always relative - even for new horns. In the case of a Martin Committee we have several things contributing to the current high price:
limited quantity of playable instruments
high demand based on the supposed magical properties.
Now, magic IS something that CAN happen between a player and his instrument but that is the catch. The player AND the horn need complementary magic to make this investment worthwhile.
I am convinced that any number of manufacturers could recreate the Committee for a lot less money. There is no magic in the brass or skills required to make one. The issue is, that too few people would buy it because they mostly want the myth first and the story behind having one is created later.