Hello DougBG
I have a 3800, what you need to do is access the "job information log" this tells you the file name of the print, when it was printed, what size paper was used, how long it took to print and how many ml was used from each cartridge.
This information can be saved as a CVS file which can be opened in Excel, it will need some editing because Excel sees 0.07ml as text and not a number so just edit the ml off. From this you can use Excel to work out how many ml's were used for each print, and if you know the cost of a cartridge you can work out the total cost of ink used for an individual print.
Hope this helps
David