I will be starting my jumbos here soon, but form what I have been told they take about $1-$1.50 per bird to get to full size. For the standard coturnix, it takes .50 to $1 to feed.
I get a game bird starter with 30% protein that costs me around $13. I feed them that for their entire life. I intend on getting a fodder system set up to help reduce some of that cost. I have never actually done the exact math though, which just gave me another idea to write about! Thanks! :D