At current prices, US$100 is fair for this trio of lenses. I have all three, and they are good. Hugo Meyer & Co. was bought out by Pentacon in the 1960s and all these three lenses were later rebadged under the Pentacon label.

The Orestor are Sonnar-derived lenses, the 135/2.8 version continued to be produced for a very very long time in many incarnations. The 100/2.8 is comparatively short-lived but by its focal length and imagining quality I use it more often. The Orestegor is more of a Tele-Tessar-related design using thin elements and is also quite excellent in imaging quality.

Do bear in mind that the 100/2.8 has manual diaphragm, while the 135/2.8 and 100/4 have preset-manual diaphragms. The yellowing should be a little more serious on the 135/2.8, but if you are shooting black-and-white it should not present itself to be a major problem.