I know I've told the group my story about buying one of these years ago for $20 out of a "junk box" at a camera show; I used it for several years and then sold it to a prominent collector, who spent fairly serious money giving it the full mechanical restoration it deserved.
And actually, the starting price isn't too crazy if you really want an ultra-fast, rangefinder-coupled 75mm lens -- your only other option is a 75/1.4 Summilux, which goes for about $1700 used at B&H, and won't fit on your screwmount camera!
Don't expect the Biotar to be as sharp as a 75 Summilux at wide apertures -- the central 1/3 of the image is reasonably sharp even wide-open, and the central 2/3 by about f/2.8, but the edges and corners have a sort of smeary appearance until you get past about f/5.6, at which point the whole image is nice and crisp. Even with these failings, it produces a nice "look" that probably would be extremely suitable for available-light portraiture, which would have been a logical application for this focal length.
One of my gallery pictures was taken with a 75/1.5 Biotar: