I recently bought a second hand K-5, and the seller recommended me to throw in a few extra bucks and get the
SMC-M 50/1.7 to go with it. I'm amazed that such a cheap lens can be this good.
The lack of AF doesn't bother me one tiny bit, neither does the fact that I need to go manual-mode on the K5,
just like in the old days. (Yes, I grew up in the film era long before AF and camera-modes were invented.)
My recommendation is go get one of these lenses and learn how your camera works without all that fancy stuff.