Personally, I've employed a "worst-case scenario" approach. I reckon that at full coverage (100%c 100%m 100%y 100%k) i'm using no more than 40cc per square meter.
If you want to get a good baseline you can always run the RIP first and then versaworks will show you how much ink will be consumed (not sure how accurate that is) and base your calculations on that amount of cc's.
So cost of cartridge / amount of cc's in cartridge (440) should give you price per cc and then multiply by amount of cc's versaworks expects to be used for the job. Obviously that is your cost and you'll want to add a margin if you're printing for profit :)
OK short answer figure $0.30 for each cc
Go to VW
Go to View Tab
Go to Drop Down
Click Job Log
Look at bottom
Expand the log
All printed jobs have a ink value
There you go - you can print - first in is first out (FIFO)
need by color double click the amount