cheap DSLR shoulder bag without breaking down camera

First of all, what IS a holster bag - are those the bags that specifically can put the camera in without breaking it down, making it easy to take out and shoot? Most of these bags don't seem to have much space for other lenses or items, which I want.

I'm looking for one of those cases that has one or two extra compartments in addition to putting the dslr with a moderate length zoom lens still attached. The dslr does not have to be face down as I see in most. I saw someone with a Nikon bag where they put the camera in as if they were putting it on a tripod or the ground, and had compartments for other lenses next to where the attached lens would be protuding. I thought all cases were like this, and I was really looking into the Mountainsmith Reflex II as I found a pretty good deal and heard good things, but the compartments look like one would have to remove the lens from the DSLR to put it in the bag.

Which shoulder bags are like this and which aren't? Which holster bags have extra storage room? What is the difference between shoulder, holster, sling, messenger, etc? I would like one where I can swing it around front, open, take out dslr, and take a picture quickly, but have room for other lenses and a flash and compartments for batteries, etc.

The camera is for a Pentax K2000, whenever I happen to find a good deal on one. Cheaper is better as it is my first case and I don't really know exactly what I want.