Do you know how much they are from Musicom? And what's the interface like?
I think you would be looking at something in the region of £20 per switch.
As with most things organ-related, you are dealing with very small production runs of specialist items, so although the cost of the actual components is relatively trivial, the unit-cost of the finished article is ridiculously high.
I can't tell you anything about the interface, but the switches that I was shown details of were pretty novel in that they came individually, and you could clip together as many as you wanted to make up a row.
Graham