Never saw a Mossberg like that before but my in-laws had the 550 and it shot to point of aim out to 50 yards with any ammo we fed it. What I found on the Mossberg was it being sold in like new condition for $130 2 years ago. Since its for your Grandma I think I would offer her $150 for each gun and see if she would take payments as you could afford them, say $50 a week or every other week. I know they made at least 750,000 of the 550 so it's a pretty common gun.
Good intentions will always be pleaded for any assumption of power. The Constitution was made to guard the people against the dangers of good intentions. There are men in all ages who mean to govern will, but they mean to govern. They promise to be good masters, but they mean to be masters.