The .50 beowulf is very similar to the .458 socom, both of which originated in 2001 as similar solutions to the same problem, stopping arabs at checkpoints in vehicles. It is designed on the AR (Armalite) platform.
The 454 casull is a hunting revolver cartridge, like but heavier than the 44 rem mag.
They don't have a lot in common. Not sure how someone could have a similar interest in them both. They are completely different.
You can get the same effect of the socom and the beowulf with any short barrel slug shotgun, in terms of stopping power on bears or badguys. If you want to penetrate steel, then the .338 mag rifles with steel bullet inserts will do this also. In addition, the .338 gives you the best accuracy downrange of all the other choices.
For hanging out in brown bear country, either the .45-70 or the .500 S&W would work quite well as a side arm, although I would not wander there without at least a .300 RUM or .338 mag.
All of these guns are in the $2000 range however. You can forget $500.
$500 is what you would pay for a cheap glock. (Cheap and glock being redundant, I know.)
That's actually a really good price. They used to be closer to $1500 in their heyday.
I think people are realizing that the 454 is "better" (more powerful) than the 44's are, but not as good as the new 500's or even the old classic 45-70s.
So there will eventually be a glut of 454's and then people will stop buying them.
Right now the magna ported 500's are hot, and everyone seems to want one.
My 44 rem mag (S&W) is painful enough even when shooting it with gloves on. So I am not planning on anything bigger anytime soon. There are no brown bears where I live, and the 44 is plenty for a black bear, mountain lion, or pack of coyotes.