The usual conversion 2000 mg sodium per teaspoon of TABLE salt. 1/4 teaspoon is usually 500 mg. If you're measuring with Diamond coasrse, 430 sounds about right for 1/4 teaspoon. BUt for your listed tV dinner, That's just over 1 teaspoon for hte meal. The FDA recommends 2000-2500 milligrams!!!( teaspoons! what a typo that was) per day total. So yes that's highish. But it's not tablespoons. You got a little excited in your division or made a typo.
But that number is not just added salt. A standard 4 oz piece of meat is 200-300 mgs sodium before any seasononing is added. A serving of "canned" vegies will be a couple of hundred mgs. An 8 oz glass of milk is 150. A biscuit will be 250 mgs, a slice of bread 200-300.
If there is mashed potato or pasta on the TV dinner, those are heavily salted so they have some flavor The sauce will have a good chunk of salt too.