Something else to consider; if it is a "magnum", then it probably just shoots 3" shells, and it could be a 1100 model. If it shot 3.5" shells, then it is probably a 11-87 "super magnum" like rukiddin said.
These shotguns vary a lot in value, but an 1100 is probably not a $550 gun, and the 11-87 could be; but they vary a lot too.
Something else to think about, is that your $550 valued bow will be a $300 bow in just a few years, and the shotgun will stay the same or go up in value.