Hi Ruben,
It's not as easy as that. Firstly, I find that I'm simply a mediocre street photographer and that there's other things I'm better at. I've done a fair bit of street photography, but my photography tends to improve if I put some time into composition, and that makes certain styles of street photography a rather, let's say non-obvious choice. (In that aspect RFF has actually been bad for me to some extent, because street photography tends to get so overhyped here.) I agree that there's some pictures I couldn't have taken with a noiser camera. But then there are others which I couldn't have taken with a non-SLR, or where the quietness of the camera was unimportant but the possibility of quick focusing was. Of course we can always say that this is a question of lack of skill, but firstly that works both ways, and secondly we can also say that there are simply better and worse tools for the job at hand. It's not the same pictures and situations in the end, of course.
To be honest if you want to get into a new, more or less modern camera system (outside the Soviet Union) with a two-body, three-lens setup it is not really that outrageous a price. I wouldn't expect a comparable Contax G system to be significantly cheaper, for example. The body alone is something like $600 for the G2.
The Kiev is one of the quietest cameras I know, at least at 1/25 and 1/10, and certainly the quietest with interchangeable lenses. It will be very difficult to find a similar camera.
However, I agree that if your main goal is silence and low price, turning towards a system SLR might not be the best solution. In that case, if quietness remains your main objective, why don't you drop the interchangeable lens requirement and try a fixed-lens leaf shutter camera? On the Canonet, which was my primary user camera for some years, focus throw is maybe 60 degrees from 0.8m to infinity, you get a pleasant finder for focusing, a good, fast lens, a quiet shutter, and the camera is small and cheap. If you want autofocus, the obvious choice would probably be the Hexar AF with its fast lens and quiet shutter and film transport. The nice thing is that both are cheap enough (or rather keep their resale value well enough) that you can just try out if it works for you. Or try a TLR.
That's a piece of praise I certainly don't deserve, but thanks anyway.
Philipp