How about this? I start with the SX SJB62-3/4:

- remove tuners, dowel headstock
- strip headstock and neck back to sealer (apparently possible with ordinary paint stripper)
- drill for 6 tuners (would standard Klusons work for VI / baritone strings? if not, what?)
- new nut blank, cut and file to suit
- new bridge - it's not string-through so I can just take the old one off - I am thinking either a Telecaster 6-saddle (if the saddles would be large enough) (top-load probably, or through-body?), or a Danelectro baritone tailpiece (a bit pricier):

Pickups - either the Tele bridge with a pickup, and/or the MIJ Jaguar pickup I have spare. The SX has 8-pole Jazz Bass style pickups but I doubt they would be appropriate for the new string spacing.
Other cosmetics like Mustang knobs etc to follow; could also do a Jag switchplate and bass cut for the pickups.
So - it would be like a hard-tail Bass VI and I reckon I could do it under $200. Anyone got any advice?
If anyone wants to take the idea and do it, I would be really happy to see the results!