Hi Guys, I thought this might be of some use to some people.
This eBay seller is selling ball-screws for very cheap - $45 for a 300mm ball-screw with ball-nut and free shipping.
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www.ebay.co.uk]
They also do end machining for an additional $15. (Either for an existing support such as the BF/BK12 or for a custom design.)
They have a range of sizes and thinking about it, it's probably around the same cost as some real Acme lead-screw with an anti-backlash lead-nut.