Off the top of my head?
Good bullets are $20 - $25 per hundred, or about .25 cents each.
Primers are around $25 per 1,000, or $2.50 per 100, or 2 1/2 cents each.
Powder is $18-$20 per pound.
7,000 grains in a pound, so if you use a 50 grain charge, you get 140 rounds per pound, or about .14 cents per round.
Looks like about .41 cents a shot, or $8.20 per box of 20 rounds.
You can probably do better by shopping around for best component prices in bulk.
rc