Keep your fingers on the pulse of the used for sale on line sites. Used jigs of all sorts come up routinely. The challenge will be finding one close enough to not need shipping.
I know of a flat AL plate that once was and would make again a fine starting jig's base. It's in western PA. I would have bought it yesterday (I was picking up my recent Paint by Todd completed job in eastern PA) had it been closer to where i was going. Price is right.
Frame building Jig - Temecula, CA - Bike Forums Post #13. As I drove to Selinsgrove PA I thought about this jig/plate and wished i had a project for it.
Were I starting out again (but with 45+ years of very part time experience) I would still want a credible flat surface before a jig. If that came about then i would consider the Alex Meade tube blocks system for the flat surface (of which one set was offered for sale only a few months ago, these are quite reasonably shipped). Or if $ were no object, Doug's jig is really cool and can take the place of drawings and complex calculations too
But that flat surface is the first big tool (as in more than two people needed to move it) to get, and becomes your standard going forward. Andy