The per-kilogram comparison is not close: sea freight wins by an order of magnitude. That is also not the comparison that matters for most decisions.
What matters is the total cost of the consignment landing when it lands. Sea freight ties up working capital for four to six weeks. It needs warehouse space at the far end. If it is late, a production line stops. Air freight is expensive freight and cheap everything else.
The rule of thumb we give clients: if the goods are worth more than roughly twenty dollars a kilogram, or if being late stops a line, run the numbers again with air. Below that, sea, and plan the lead time honestly.