I used the Bronica for a few days a few years ago, and it's quite fun to use. Congrats. Well, what I'm about to say is not a "cost-effective" solution short-term, but you may thank me later: if you have the money, get a Metz 54 flash.
I got one over a year ago, with the Canon module, but also got the standard module soon thereafter. It's a beauty. I can use it with any camera that has X-synch and I couldn't be happier. I hardly use flash, but it was a justified cost because I did two wedding jobs last year (I'm not a professional photographer, but the gigs came up, and can't say no to that). Metz flashes are an absolute beauty. And you could buy dedicated modules later if you want to; the head can be adjusted for the focal length, and it can automatically compensate for the format you're using (35mm, APS-C, 6x6); it has its own "automatic" exposure setting, so if you use X-sync with it, you don't even have to worry about manual settings much. It's not "cheap", but in the long term you will see that it may be your only flash for all your cameras.
Just a thought.