There is none.
TMP has specified that Antarctica and the Arctic are willing to accept anything as payment(specifically items that have little to no real value to the seller - what would Antarctica do with billions of yen worth of origami or sushi?)
Countries could pay with dirt...I prefer paying with seawater - no cost to the buyer to ship as payment.
So, then, the question becomes...How many gallons of sea water is an Akagi worth?