A $400 fridge/freezer is well worth the money, IF your intention is to stay remote for longer periods of time, i.e. overlanding. Also if you prefer to not have to purchase ice at regular intervals and still keep your food cold.
Actually, at $400, that is cheap. My ARB was closer to $900 and with the sliding mount, cover bag and better wiring kit, it was well over that amount. The $400 units, such as those from Rough Country are a steal.
If your intent is to primarily only be out for 2-3 days, then by all means purchase a regular cooler and use pre-chill and ice. It's more your intended purpose that decides your needs just like any modification you make to your vehicle.