where to start?

[Jonathan]

But I was giving easy options that could be bought off the shelf at sensible money

Welcome to buy one from my shelf...

Think I'd also go with a higher 20mm pitch if being used solely for cutting woods n plastics

Same, but you couldn't get 20mm pitch from eBay seller last time I checked. I would have done the same otherwise.
Thinking about it since end machining isn't strictly neccecary with a rotating ballnut setup (helps, but I reckon you could do it without by making mounts that clamp the screws, rather like the mounts for round rails) you could buy the 20mm pitch ballscrew from Zapp without spending £7.5*10^99 on end machining. This one:

http://www.zappautomation.co.uk/r161...121c620028629f

or

http://www.zappautomation.co.uk/r202...121c620028629f


Oh, just noticed the ball-nuts are a bit pricey ... shame.
I'd love to try it with some 20mm pitch screws and big motors / servos and see just how fast you can get with rotating nuts.