A 97 Cocker has a lot of meat to it, so it's a good base as a milling project. That, and you'll still find people out there that prefer a right feed gun rather than a vertical feed. It's a niche market. You're either going to find people offering you peanuts for it, or you'll find someone offering you what may seem like too much. Of course, you'll get far more "peanuts" offers than the other.
I'm going to disagree on SKI008's assessment of the Apex effect. I wasn't a believer until I picked one up. Playing woods and big games, the usefulness of the Apex can't be overstated. You get literally twice the range. Yes, you don't have the velocity at those ranges you would at "conventional" ranges. But, you get the other side to go to cover from much further away. If they're never out of cover to fire at you, and you can close to a distance you can get a break on them at, that's worthwhile. You can get breaks at long range, too, you just have to hit something hard - like a marker, goggles, hands, things like that. The other thing a lot of folks don't catch is the bizarre ability to shoot a curve ball. Again, I didn't buy into it until last spring at an event at Sherwood in Indiana. I shot sideways at a guy who was tucked into a building, and got a perfect curve shot that arced sideways into his building, through his window, and took him out. It takes some practice and some luck to get those shots, but they're memorable when they happen.
You may also want to browse the BST here for tanks. There's some very good deals to be found. Just remember that any HP cylinder has a 15 year total life span, after which it has to be discarded. You don't want to buy someone's tank from 1999, and be stuck looking for a new bottle in a couple years!