According to the BJP the Yashica lenses were surprisingly good and a worthy alternative to the Zeiss ones.
Shush. Do you want everybody and his dog to find out? We've enough problems with good film lenses being pushed up on Ebay without this kind of irresponsible talk.
My first Yashica camera (the still-going-strong FX-3) came with a Yashica DSB lens, which was pretty mediocre. It took me a long while before I learned that the ML series lenses were significantly better, with some approaching Zeiss quality. I've now got most of the MLs in the 21mm to 300mm range, including most of the zooms. The 28-85 is very good indeed, and I have some shots where it was only my photo notebook which told me which were taken with the Yashica 28-85 lens and which were the 50mm Planar used on the same outing. The 50/1.4ML is an excellent performer, though strangely enough, I've seen the 50/1.7 Planar go for less, and the P50 is definitely the best 50mm lens I have ever used. The 75-210ML is also a good lightweight zoom. The pair of these zooms make a good go-everywhere pair.