Originally posted by auto210035 In particular, I find that pentax lens tends to be more expensive than canon and nikon, but I'm forced to go with pentax because of their AA batteries.
I have a simple solution for you to get quality night shots without a flash. Discard your Pentax, buy a Canon body, with a battery pack, and then invest in a Canon EF 85mm f/1.2. The lens itself will go for no less than $2200.. certainly quite cheaper than any pentax lens. Do your research!
As Marc has said, you are more or less asking for the impossible. Forget about 2.8 with the K-x for what you want to do. The closest thing I could imagine you getting somewhere with, on your mission, would be with a K20D or K7 with an FA* 85/1.4. Don't expect this to be easy to find.
As for manual focus, an A* 135/1.8 exists but this could be also very hard to find.