make sure you actually check the focus before you take serious shots with it
a jupiter 9 that's been calibrated for non russian rangefinder cameras will focus improperly on a fed. at 85mm and f2 that could become a huge problem.
shimming it to match your fed is pretty simple work though.
the prices of old leica screwmounts seems to fluctuate every few years, but recently i think that the appearance of all the new digital m's like the m9, m, m monochrome, etc.. have been pushing down barnack prices and pushing up leica lens prices