There is a old rule of thumb for this which works out in a general way. However this must be tempered with the knowledge that companies have different hedging arrangements and different places have quite wide ranges of prices.
As a general rule then : Multiply the cost of a barrel of Dubai Crude by 10 and this gives you the cost of a ton (1000kg / 1250 liters) of Jet Fuel.
Todays figures show this approximation holds.
Singapore Jet Fuel = US$24.65 per barrel
A Barrel (in oil terms is, as we all know) = 158.98729 liters.
This gives (at an average SG of 0.8) US$0.15533c per liter == US$194.16 per ton.
Hope this helps.
MG