Oh come on ... if someone came on here saying they wanted to buy a processor off ebay the answer would be a resounding ... "build it yourself".
Exactly what I want to do, mechanical side I can do with me eyes shut but would probably need some help with the electronics.
I'm thinking of making molds for castings, centrifuge bowl for one.
As offered before, happy to help where I can.
Electronics aren't my strong point either, but if you buy completed boards, it's really just a matter of carefully and methodically wiring them together. If it was difficult, I wouldn't be able to do it! Based on my recent purchase I recon you could build one for about 150 - 160 quid now.
Maximum size you'll get on the bed of a typical cheap printer is around 200 x 200 x 140 high, probably a little small for a centrifuge bowl. If you're thinking of an investment casting, what about a makeshift lathe (drill, vice etc) and making the pattern in polystyrene?