The cost is not $0.00 , but close
I've been reloading ammo and casting bullets since 1975. I waded through a 1 semester course about 'Engineering Economics' , change my own oil, rotate tires, and do my own vehicle maintenance until the "computer" gets involved. All of this is done to save money. How you calculate the savings is your problem.
This is the cost of 50 rounds of 9 MM ammo loaded with 130 gr cast lead bullet. The brass is range pickup, and lead is mined from the back stop / berm. When a new mold is bought, enough bullets are cast to recoup the cost of the mold the first time. Cost of 50 rounds of 9 MM is $2.05 per box, about the same price as 22 LR bought on sale. I'm retired, have $0.00 earned income, and my time is mine unless you want me to work for you. But I don't think you can afford my labor rate, if you can, I'll raise it.
Close rule of thumb: 1,000 cast bullets exceeds cost of any 6-cavity mold. An exception: 45-70 mold, handles and sizer body was $145 delivered. Cast .458 diameter bullets are $140 per 500 plus shipping. So about 500 bullets paid for the new caliber setup.
Copy and paste from an Excel spread sheet looks really ugly and hard to read.
Caliber: 9 MM Std. Cost
Powder / lb. $21.00
Powder chrg, gr. 3.6 cost = $0.54
Bullets / 1C $1 cost = $0.50
Primers / 1M $20 cost = $1.00
Brass / 1C 0 cost = $0.00
Ammo count 50 Total cost = $2.04