A sensible price is whatever the market is ready to pay for it.
There is no technical reason why the Nikkor should be much cheaper, than, say a pre-asph Summilux from the early 70s. Yet nobody wonders about the Summilux prices.
You want it now at low risk, Kevin has it - he is very reliable and you can count on his descriptions.... If you can wait and take some risk: go on ebay. I bought my last one (Tokyo) for less than US 300 incl shipping.
One thing you could try is buy a Nicca/50-1.4 combo and sell the camera afterwards. For some reason they show up cheap, occasionally.
Used price will strongly depend on version: early Tokyo or 5005xxx lenses, vs. Japan all chrome, vs. late black rim lenses.
Cheers,
Roland.