The industar 50-2 is a tiny, tiny lens... it is smaller than the Pentax pancake. Difficult to focus because of the tiny focus ring and is a 3.5 aperture lens.
For a cheap, but very good lens for your display/use of the camera I would recommend the Helios 44M or any of the 44- variants.... It is not only looks good on the camera but it is a great lens for the money. At F2 it is a great portrait shooter.
They usually run about the same as the industar 50-2
I have both of them and the Helios is one of my most used lenses on my K20d.
Here is a shot of it on a camera.