Demand and supply, simple as that. Good luck with that. You might nab one off ebay for cheap if you get lucky. You might get lucky here or on BUG (Bronica Users Group), for that matter. For $150 it had better be absolutely pristine.
KEH right now has an EX+ for $109, and an EX for $99. That's pretty much what they've been there for several years now. I suppose a BGN would be 10 or so bucks less if they had one, and a UG another 10 or 20 less, always depending on actual condition, of course.
You don't have to have to have the WL finder to shoot waistlevel, of course. You can just take off your prism and be careful to not scratch the screen.