The Micro-Nikkor P Auto 55mm f/3.5 lens is a manual focus macro lens produced from 1971 to 1973. I bought my copy some years back for 500 DKK - roughly 70 USD - and even for vintage manual focus lenses that's cheap.
Out of the box it offers a reproduction ratio of 1:2 but with a cheap extension ring (M1, M2) you can get to a 1:1 reproduction - which means that the image on the sensor is the same size as the subject in real life. In short, you can get closer to the subject - which is what a macro lens is for.
Many people also use this lens as a standard lens, but I don't. It's supposed to be good, but I have plenty of other 50-ish mm lenses to choose from.