There are many manufacturers that provided lenses for LTM and Exakta mount. I don't know that these are any better than the ones made by Leitz, Canon, Nikon, etc, but I do know that many of them are now ludicrously expensive.
I suppose this is because they are now very scarce, but I have never bought into the notion that scarcity necessarily means value. Things like this tend to be scarce because they didn't originally sell very well. I hate being a curmudgeon, but while this could happen because the lens was so good that it needed to have an unattractively high price, but other less appealing reasons are more likely, I think.
Cheers,
Dez