A decent luthier could build you something close to an SLB-100 for a whole lot less. I have a mate who's a carpenter and we were considering a 4/4 EUB custom build using commercially available neck, bridge, and tailpiece with a carved SLB-100 style body (i.e., removable treble and bass side bouts) using very high quality wood. It would have been passive, but let's face it the pre-amp has never been the selling point of any of the SLBs, even the 300. He quoted £1000 for the work (parts on top of that), but it was before lockdown and wood has gone up a bit since then (and I found an SLB-100 at £1200 used which made more sense than a 12-month lead time). But at even £2k it would save you £3k and probably still lose a lot less money if you needed to sell.