Hi Don,
I had these switches in mind:
https://nz.element14.com/honeywell/bzc-2rq1-a2/switch-basic-top-pin-plunger/dp/1525197Note this is the New Zealand site of Element14 so the price is in NZD. Works out to about $13 USD. Element14
I think might be called Newark in the US.
I thought that if you could drill a small hole in the plunger and glue in a 1/8 bit of wire as a probe extension.
All three switches could be attached to a flat plate of some description which would have a shank that fitted
in your spindle.
These switches are pretty good quality and 'guess' you could get 0.001 repeatability with them. One of the features of
these switches is about 5mm of overrun. That is the travel that the plunger can make AFTER the switch event without
bottoming out and damaging itself.
As you can see I'm thinking that you could make a thee axis probe for under $50. I imagine that there would be some
coding required, but that is time and brain power intensive, no dollars involved!
Craig