It's all a matter of perspective. Some think the word "cheap" means something else than others. When I decided to swap a NV4500 into my crew cab, it took me 1 month to find one on a good deal (once again, it was a good deal from my perspective), and I found 4 in the Denver to CO Springs areas that I felt like were good candidates for my particular swap. Sometimes, when you find something real cheap, it just means you are going to pay on the back-end for stuff like a rebuild on the tranny, and in the end you pay the same as what all the other tranny's are going for.
If it's something you really want, you will find what you are looking for, at a price you want to spend. A NV3500 would work just fine in your K5 and what it seems like you use it for. Scott would need a 4500 for sure in a big one ton with a big block and possibly towing a little bit too . And once again, really not that hard to find if you start looking real hard