The Nikon NIKKOR Z 85mm f/1.8 S is the most cost-effective choice for low light portraits right now. Technical tests show it outperforms older f/1.4 glass in micro-contrast and edge sharpness when wide open. You dont always need f/1.2 to get great bokeh if the lens design handles transitions well. Two tips for you:

• Focus on lens coatings like Nano Crystal or Arneo to reduce flare in low light situations with street lamps or studio backlights.
• If you are on a budget, the Nikon AF-S NIKKOR 85mm f/1.8G is still a beast on an adapter and leaves you plenty of cash for lighting gear. Sharpness is basically identical to more expensive F-mount options for real world use.

I've used the Nikon 50mm f/1.4G for portraits since 2010. Be careful wide open, but great value.