Hm. For a new stainless-steel ("all-weather") Mini-14 you're looking at $800 and up. Factor in the cost of mags (steel 20-rounders are $50 from J&G Gun Sales), and recognizing that you'd end up with a gun that won't win any accuracy contests and is rarely as, much less often more, accurate than an AR, and I have to wonder why one would look into a Mini-14 as a defensive rifle. It's not a fighting rifle.
If it were a lower price than I'd say go for it; you're already running into AR-territory, and will get into nicer AR territory if you plan on getting any number of magazines for it.
Just keep in mind that stainless steel is not stainfree steel. My Leatherman Wave taught me that lesson very quickly on a diving weekend.
I strongly suggest getting a Mossberg 500 Mariner, for a couple big reasons. First, it's purpose built. It'll handle salt water fine, if you wash it. Second, it's cheap: $385 at Able Ammo. I think that's better suited to your needs than a rifle would be, and if you needed longer shots you can easily get a longer barrel for slugs Maricoted as well. The
only reason I'm suggesting the Mossberg over the Remington is price; Mossberg is simply a better "budget" gun.
If you want a rifle, specifically, than get a rifle. For the price you're already looking at, I suggest an ADS M4 from
G&R Tactical. Grant's a good guy and can customize orders if you want. But if you just want to be armed with something better than a handgun, and don't want to break the bank doing it, I suggest the Mossy.