If your goal is to find a used camera to keep as a backup, then the sources recommended above will give you a lot to think about. (I've used B&H many times, and highly recommend them.) If the point is to use the experience to learn about pawn shops, then have fun exploring.
If it were me, given that cameras have become so inexpensive, I'd avoid used, and buy a new one that has the features you want in a backup camera, but provides it in a different footprint. By that I mean make the second camera a pocket-sized camera, or even a point-and-shoot that has features you'll like.
My spouse has a degree in commercial photography, and is an extraordinary photographer. Owns a ton of camera gear, the main part of which is a top of the line Nikon DSLR with numerous lenses, and many, many gadgets and such to go with it. Second to that one (and a recent purchase) is a high-end Sony point-and-shoot. And third in line is a Leica glass-lens pocket camera. Adding my own cameras to the mix is a long-lens Nikon point-and-shoot, and last of all is a lowly, but very convenient Nikon CoolPix pocket camera I've owned for about ten years. When we travel, a constant question is "Which camera(s) are you taking?" I carry both of mine, and let my spouse deal with the tonnage packed into those heavy camera bags. I figure if you want to use it, you have to schlep it.
None of this answers your questions, but it may give you some food for thought. You may want to consider what you'll use a second camera for. At our house the other cameras are used when the big set up is too much to carry around, or when a smaller camera is a better fit for the occasion. And we won't talk about the cell phone cameras, which take better snapshots than anything else in the house.
Have fun shopping!
Dave
