Going back to the original post, this really is like comparing apples to oranges. If you want an economical well made double, good for small to medium game with loaded ammo available then the 20 gauge RBL looks to be a pretty good choice.
The 577BPE will cost more to get into but you will be able to get every penny back and probably much more when you recycle it. Buying used the gun will not fit you perfectly but you will have a pride of ownership of a weapon built by arguably the best craftsman to ever put purpose to wood and steel. You will have to craft your own ammo but that will only add to the satisfaction of owning and using a piece of history. You will not only be able to use the gun on small and medium game but properly loaded, DG as well.
Well, which do you like apples or oranges?