I have been thinking along similar lines though at 35mm equivalent.
Why not try a cheap 35mm camera with an ok lens before spending your $$$? eg, a Yashica 230AF with the 28mm prime will run under $100 inc battery and you see if you like the auto experience as well. That will get you comfortable with the 28 (which is really a lot wider than I thought it was going to be. I can't quite get my head around it which leads me back to my 35)
Or, perhaps a Fuji GA645WI plus $500 worth of film/chems/paper?
Maybe it doesn't really matter? Both your listed options are good after all.
If you haven't made the purchase yet, my two cents is why not save a whole lot of cash and get the lens for the 645. That way you can play with that camera (I love the negatives a whole bunch more than any of my 35mm rangefinder or SLR stuff) for awhile and experience that system for awhile.
I understand it sounds like your having a very serious rangefinder gas attack (mine is fortunately controlled through medication for now), but I will repeat that I understand your love for the rangefinders, but I can almost guarrantee that you will start really appreciating your 645 if you use it more. That big, big negative is wonderful to work with, but I do love the pictures I can get out of my Lynx.......
Final thought, now that I have an operable rangefinder press camera......I really, REALLY want to step up to a 4x5.......perhaps you money will be better served by building it up for one of the larger format rangefinders......afterall, I think you can tell that everyone on this site has pretty much gone from 35mm whatever to a larger and larger format camera.
Good luck in your very hard decision.....been there, well about four days ago!!!