If you want something a bit shorter, the Nikon 105mm 2.5 non-Ai/Ai/Ai-S are all very sharp lenses wide open on M43. For a bit less, you can get a Nikon 100mm 2.8 Series-E for a bit cheaper and is also very sharp (I own this lens).
Maybe you're looking at two different lenses. but wow, 100€ is a lot of money for a 135mm f2.8, even if it does say Nikon or Nikkor on the front. Seems to me you're paying for a great name and sharpness that you won't necessarily use for portraits. How much is a Canon FD 135, a Konica AR, or Olympus OM 135 in your marketplace?