304 food grade stainless steel is not recommended to contact with saltwater, but it is the most used stainless steel. Other than being marine grade, 316 is stronger too. I imagine the price of them would be quite a bit difference.

To be pedantic, a 304L sink with 309 filler rod would be the best material. Unless you plan to submit the sink to large tensile stresses or to immersed  the sink in concentrated salt solutions at elevated temperatures, 304 will be fine. For room temperature and moderate aqueous solutions of PH, 304L is preferred, which is why it's used for all food-grade applications.

My sink is 316L and the back splash is 304L. They have been in use many years and subjected to the same conditions, and there is no visible difference. The 304 should work fine. However, 316L is really only necessary in the most demanding circumstances, and it is quite a bit more expensive.

I had two four ft stainless steel sinks which is made a number of years ago, and didn't know there were different types of stainless steel. The sinks rusted, particularly near the drains. I don't recall if the drains rusted, but I think they did. I remember that chlorides can cause rusting problems unless you specify the corrosion SS for the job. In spite of that, I now use one of the two sinks without a drain and occasionally sand it to get rid of the rust. I've wondered if I could shine the thing up and then coat it with a clear finish.

I agree that a sink could easily be made to look good, that would be cheaper and easier to build without using stainless. Down the road if you move houses or switch to digital, you could just trash the sink. It's hard to scrape a SS sink because of the money invested.

Austenitic stainless steels