A local shop just started rentals (granted, digital). A Nikon D7100 they sell for $1100 rents for $180 per week. So about 16% of the new price per week. I have no intention of arguing for or against their rental price, other than to say it's probably typical.
I suspect you would need at least a week, maybe 2, to really get to know a Leica. So if you buy one, you have some room to sell it for less.
If you want to see if you using a RF, and don't want to take the plunge for a Leica, buy a good, CLAd Canon GIII. Personally, I think that will be a better tool for evaluation than a FED or Zorki (absent the interchangeable lens).