Hello everyone, as a counterpoint to the lovely looking and evidently very high quality offerings that others have posted here, I offer my own work-in-progress as an example of an unlovely but functional approach.
Approximate costs so far:
Keyboards £60 for all three
Pedalboard £50 (included a bench, not the one in the picture which is home made)
Midification of all above £70
Stops control £125
Foot pistons £20 for the whole assembly
Expression Pedals £10 each
The three keyboards are still recovering from having been stored in someone's damp garage for a long time before I acquired them. Since I'm basing this setup on the Hereford 46, I will probably replace the three 61 note manuals with 4x58 note ones that I have but are as yet unmidified. Sensing on the keyboards is optical and the pedals use reed switches and magnets. All the encoding/decoding hardware is of my own design and construction.
The foot pistons consist mainly of 22mm plumbing components.
The arcade switch based stops control system I will write up (as promised before) in the 'DIY consoles/MIDI' section once I'm reasonably sure that the code and hardware is bug-free (so far so good).
Of course, putting all this together has also cost a lot of time (probably many hundreds of hours in all) and a fair bit of un-costed development work in trying out different, and not always successful approaches to the mechanics of the keyboards (all were ex-tracker) and midification.
The other thing to bear in mind is that the system has been put together piecemeal over time, and quite evidently isn't finished yet.
Hopefully all this may offer some encouragement to those who don't want to spend (or can't afford) the money that would be needed for a top class bespoke system or are daunted (as I was initially) by the scale of the enterprise as a DIY venture.