My comment may look surprising but what is the benefit of a marine cooktop v.s. an household one? This year I installed 2 stainless steel 2 burners household cooktops aboard, one in the galley and one outside on the flybridge and it cost me less than 150$ (Canadian $).
L
Deep inside that "All Stainless" household stove there are parts that are not made of stainless. Those parts will rust when exposed to the Salt air environment. You have your boat quite a long way from the Ocean, so yours will last a few years longer, but the next owner of your boat will ask for a discount on the price when he identifies the stove as not being a true marine grade item.
My home is 100 ft from the salt water. Until I found a BBQ manufacturer that gave me a guarantee that NO PART of my BBQ were made from any corrosive material, I would get 2 years from a domestic BBQ, especially the ones that looked to be "All Stainless" The parts that held the burners in place were the most frustrating, as there were no replacement parts easily available. I had to buy a whole new BBQ to overcome that problem. The one I have now, guaranteed, remember, looks exactly like the day I bought it, whenever I clean it.
The Marine grade propane stove I have on my boat, a Force Ten, 2 burner drop in top, is now over 20 yrs old and when I clean it, looks and works as good as the day I bought it
The Marine grade Fab-All Diesel stove I have, 23 yrs old, also looks and operates as new.
There are good reasons for the higher prices on truly "Marine" grade items. Stoves are just one of many.