From my recently late father's collection I have his mostly machined Clarkson 1/12th scale Sanderson Beam Engine.
Same as this one:
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Not sure if they are still in business, but looking at the prices of kits from Stuart-Turner their machined beam engine kit is around £900 and unmachined at ~£250Our engine has had the cylinder and valve block machined, the main flywheel, crankshaft, base, axle, and lots of other bits done.
With that in mind I reckon on a price of £350 being reasonable.
If anyone is interested I'll get some photos done. I should really keep it and complete it, but would probably never find the time.
Lee
07768 656 382