>>3923472>which I hope to be cheaper than new mirrorless lensesWell... kinda.
As an example, lets take a look at a couple of Carl Zeiss Jena Pancolar lenses:
>Pancolar 50mm F/1.8A very nice nifty fifty, can be yours around $100-$150. I own one, and can recommend.
>Pancolar 55mm F/1.4Obviously going to be more expensive given the brighter aperture, right. But how much more expensive could it be? Well, ebay has three currently on sale going between... $2,699 and $2,999
So yeah, not always the cheapest. But in general, particularly between 50mm to 135mm, there's a ton of very nice options available.