Originally posted by stlpen I am curious about why prices go up or down for lenses?
In simple words, the price of new lenses is going up and up, and the last 10 years has shown that it is not going down. Beyond a lens is an investment; it does not loose value like a car or like a camera body. A good quality second hand lens can be purchased about 85-90% of the price of the same new lens even after a few years.
There is in parallel a broad market of used lenses, especially for Pentax because Pentax continues to use the same K-mount for years. In the 2nd hand market, there are both very expensive lenses (like the FA*85mm f1.4) and much cheaper lenses. Typically MF prime lenses are the cheapest and many are excellent bargains.
You are after 2 different lenses: 35mm f2.8 and 50mm f1.4. If you like to shoot in lights, I would go for the 50mm f1.4 because of the larger aperture. If you want a wider lens for action shots in daytime, the 35m f2.8 would be good choice. Both are well priced especially 2nd hand and the PF markeplace is a good place to search.
Hope that the comments may help....