1. I have paid $200-300 for a pup from proven parents, and it is absolutely a gamble. Regardless of the line of dogs, if someone says they don't have any culls in their litters then they are only kidding themselves. If a guy is honest with himself and recognizes a cull for what it is, every litter will probably have one or more culls. The tighter the line breeding, the fewer number of culls, generally speaking. Get too close with the breeding, and then the number of culls will increase.
I have a pup getting close to a year old, paid $300 plus shipping to have it sent out here from Michigan. Paid about $700 total, AKC registered, and I am starting to think she will not make the cut, cull. That sucks. The breeder did give me a guarantee, so I can get another pup to start over with, and will have to pay shipping, again.
3. I consider a finished dog one that has peaked in his potential. He must have been given the opportunities to learn, and hunted hard. If he is 6 y/o and still has a few holes, well, he may not be perfect, but he is finished. A three y/o that is solid may still not be finished.
A three y/o that is finished should be valued more than a four y/o due to the fact that he would have more life expectancy ahead of him. But, the four y/o may have had more hunting experience and be a little wiser, so he may be the better dog. Sorry, I guess I don't have a definite answer on that one. Dogs are all individuals.