The official IATA website has a really interesting chart were you can see an up to date average of the Jet A fuel prices across the globe. This gives great insight into how much airlines are paying on average.
To calculate the total cost I recommend you look at ccts/gal. You will have to calculate how many gallons of Jet A you are using by dividing lbs by a factor ranging from 6.55 to 6.85 depending on temperature. Once you get your gallons you just multiply your gallons by (Price of Jet A per gallon/100) This is because the listing is in cents not dollars so you will need to convert to dollars.
I have an example right here
I use 36194 gal Jet A
The average price of Jet from the region I am flying out of is 211.5ccts/gal
My equation will therefore look like this
So my flight is costing me $76,550.31 in fuel.
Of course this is just fuel cost and there are a lot more charges on a flight such as landing fees, flight taxes, air crew costs, etc but this just will give you a valuable part of calculating how much your IF flight would cost in the real world from just fuel alone.
Fuel Pricing source: http://www.iata.org/publications/economics/fuel-monitor/Pages/index.aspx