Spencer Chase is correct that this spring can be fabricated by
individuals with fairly rudimentary skills and not a small amount
of patience. It boils down to what is your time worth to get an
acceptable result? In my own experience, it has been a frequently
frustrating process. Long ago I purchased small coils of several
gauges of piano and harpsichord wire for the purpose of making
one-off springs, and usually have a size that will work. And if
not, my local piano tech will help me out. However the relative
complexity of this particular spring gives me pause.

I have received a quote from the first company I sent a request
to; for the assumed quantity of 100 pieces, their quote is $25 each.
My sense is that this is at the upper limit of what the market would
bear for this. Obviously, I'm not planning on investing $2500 without
guaranteed sales, which is why I'm suggesting a subscription based
model.

At the same time, I would hope to be able to get the cost closer
to $10 so that getting two or three to have spares on-hand would be
attractive. With that in mind, I will submit RFQs to additional
companies in hopes of getting the price to a more reasonable point.

John Grant