I would say theres two reasons for the price... There is a mounting kit that is very sturdy that the bags fit into which does keep them from moving around and away from the exhaust. Also, I would say these are closer to a hard bag, than a traditional soft bag. They are heavy, solid, and while the outside is "sky" fabric, they underlining construction has some solid pieces. I definitely would suggest seeing them before you buy, but these are definitely not like the tourmaster or cortech bags which I would consider true soft saddle bags. Hope that makes sense!
Also, on my 650R I traded in for the Monster, I had hard side bags. They were a combo of a Mounting Kit from SW Moltec and Givi e21 bags. This setup cost me somewhere in the $400 price range, and was not a clean "stock" looking install. In my opinion, the DP Bags for the Monster 1100/696 look better, look designed for the bike, and provide great functionality. Honestly I was bummed not to buy them, but if I couldnt carry my laptop, at that point, there was no need to buy them. As I said, if you can go see them, feel them, I think you will see why they cost more. But then again. I think SW Moltec makes a rack kit (check twisted throttle) for softbags for the monster 1100/696. The rack is somethiing like $100, then you can put givi, tourmaster/cortec, or any other strapable softbag on that you want. The quality of the bag is what is the difference here I think. The DP parts felt more like a hardbag made with sky fabric than they did a traditional soft bag