I used to see those 45/70 revolvers advertised in gun magazines. Don’t recall the price.
Academy Sports has a Magnum Research pistol in a .45-70 for $1,079.
Too much gun for me. Personally, I wouldn't probably go above a .41 magnum. The gun will do its job if the shooter does his. A .500 S&W doesn't do any good if the shooter flinches and pulls the shot. It will make a big hole in whatever the bullet finally hits but it might not be the target.