#1 Between the two (80mm vs 65mm) one is not better than the other. They are both like specific tools used for specific things. What will you be using the spotting scope for? Are you doing most of your hunting in the timber, doing back country hunts? Or is most of it out of a truck or in the open sage/crp? Because depending on your type of hunting, the situation will determine which is better.
#2 What is the price difference between HD and non HD. On the one hand if you have saved up enough for a non HD might as well keep on saving. But on the other hand most people cant tell the difference between the two. The HD will not have as much Chromatic Aberation, so if you notice that then yes pay for the HD. If you don't notice the CA then get the non-HD version. Both are clear and do well at low light and have a crisp image. But the HD version has a lower Chromatic Aboration.