I've been wanting to pick up an old Rigid 300 threader, those are good machines. As you say, they are usually pricy even well used.
Manuel Quiroga had one in his shop. IIRC he'd had trouble with being able to grip hot steel well in the 3 jaw quick chuck and was planning to build collets to use with it.
Lately I've been planning to try twisting with my 18" Hendey lathe. I would use the lowest backgear speed and build some collets to keep hot steel out of the chuck jaws. I saw a vid in which a billet was twisted very nicely with a big old lathe.