Hi

TBI are not ground, they are precision rolled and supposedly are to JIS C5 standard, but they are not ground....good for the price but they are not ground.

I would not even consider buying a ballscrew second-hand. Between the right length, diameter, pitch, ends machining, preload, .... you'll simply never find the perfect match.
You are correct, its near impossible to get a perfect match but you can get close. I got three 32mm C5 BNFN double nut THK screws and six THK FK25 fixed end mounts for $1000USD including
shipping to New Zealand. Perfect, not quite, but pretty damned good. Would have cost $10,000 new.

You might not consider second hand because you cannot get the perfect dimensions but then you have to take the quality hit to get parts you can afford which are dimensionally perfect. Your choice.

I chose otherwise. Lars has chosen similarly.

Craig