Osprey has a nice honest William Evans 450/400 at $20K.
If you can stretch your budget a bit, you may be surprised at your options.
The biggest double I have ever shot myself is a 470 and the recoil was robust but not unmanageable. About on par with my 425 Westley but it does have a steel butt.
You may want to consider a 450/400 or as Nordmann suggests, a .375 simply because with a 470 or 500 you will be overgunned for anything but big brown bears in NA, and it is a big step up in the recoil department. Remember, if the recoil is objectionable, you may have a hard time developing a lighter load which regulates satisfactorily.
It would be a shame to get into a first double and not fully enjoy the experience. I bet a medium double would be perfect for the hunting you plan for and there is always the option of moving up to the bigger rifle if you find doubles to your liking...and lets face it, who doesn't want another double rifle?