If you’re considering used, I highly recommend Keith Williamson of Online Watch Tools. He has great integrity, carries top-notch used tools priced fairly, knows his stuff, and is willing to share his knowledge freely. I bought a nearly complete used Leinen Reform kit on eBay. It was in great shape, but was missing its tailstock. Keith pointed me to one listed on eBay and got nothing out of the deal. As a result it turned out great, but I could still be searching for a tailstock that would work. Piecing together a precision lathe is risky, takes time, and by the time you’re done, you will likely spend more than if you’d bit the bullet and gotten a clean complete set. I got lucky, you can too, but you may not.
Here’s a link to Keith’s site. I understand he’s in the process of moving, so he may be slower to respond than usual.