15m Industrial Plasma Cutter

Anything useful here?
www.zappautomation.co.uk/machines/individual-parts.html

Or maybe this, you could have it tomorrow with Prime:
www.amazon.co.uk/KKmoon-Stainless-Actuat...ission/dp/B07HGS6PS1

And for the magnetic breakaway:
www.amazon.co.uk/Valeny-Magnetic-Buttons...andbag/dp/B07PY6LD31

Jarman wrote:

I'm also wondering if I can throw together an extremely simplified version eg. no variable z axis height/magnetic breakaway or any of that. And just accept that the quality won't be fantastic, but at least it will get done.

That is a big no no, you will regret that during testing and tuning, before you make any usable cuts.
There are plenty of options, and you can build your own floating head in half a day, using drawer slides with ball bearings. Built plenty of them and they do work perfectly ( well untill some of that fine dust gets to those balls, then some major leaning is needed ) granted you turn their slots to the back side to prevent the above. Find a hydraulic repair shop, there must be one near you ( there are 2 in my town with 110000 people ), they have shafts at any diameter in 6 meter lengths, so get 1 meter of 14 or 16 or 20mm shaft at around 30 to 40 euro, should be enough for a Z axis plus floating part ( floating part needs about 1 cm of movement, just enough to trigget the floating switch or sensor ), find a shop for bearings as they must have linear bearings for round rails/shafts, get 8 of them at 5 to 7 euro a piece, and a switch, 4 aluminium plates at 10 to 15 by 4 to 6 cm with 3 holes on them, allthread or a 20 to 30 cm long M6 or M8 or M10 screw, and in a day you have a fully functional Z axis with probe.
That makes 2 options, both cheap and very quick with hand tools and a bit of persistance.
And just in case you think that drawer slides are to thin or to flimsy, get two of them and mount them at 90 degrees to each other, you will be amazed at how stiff that becomes.

I have never even seen a plasma cutter, so take this idea as purely theoretical.

But I think this could make a good floating mount:
uk.rs-online.com/web/p/slide-unit-actuators/1244615/
The idea being that after the probe the air pressure can be increased to lock the head down to avoid false-tripping by vibration.

There are definitely cheaper ways than the pneumatic cylinder. I only really proposed that as an off-the-shelf unit to save time.
The cylinders also have provision for mounting solid state switches in a range of styles and types: uk.rs-online.com/web/c/?sra=oss&r=t&searchTerm=D-M9