Agree with everything you say, and you have a specific goal in mind for what you are doing with your home raised cows and bulls. And a damned good job of it too. But still, IF you ran a commercial herd to sell calves every year..british, continentals and various and sundry mixes of the 2... and IF it did cost you the $3100 chart the says it takes to get the 1st calf from your retained heifer. And if you did buy some $1500 heifers or $2k bred cows and had to cull a couple, you'd still be money ahead IF your goal is to raise a calf to sell every year. At sale barns across the country today, there are cows or heifers sold as good or better than any we could raise.I've raised several, and bought several, both registered and commercial.
Like somebody already said in a comment, there is a cull factor with both.
Seems to me that it's higher culling with purchased animals both heifers and cows than when you retain heifers.
To me there's too much variation across the board, anybody would just have to plug in their own figures. There's expense to both.
When you buy, it's luck of the draw, even if buying from a reliable source.
When you retain it's still somewhat of risk because they don't all turn out, but hopefully a higher percentage will stay in the herd longer. Those animals that you know you can track progress and build on it.
I also understand that the bottom line is not the do-all end-all reason a lot of people raise cattle. Personal satisfaction in what a man does or creates often has an intangible value that transcends market value. All I am saying is, if a person does retain heifers at that $3100 cost, they could undeniably buy one as good or better for less money, and with quicker returns. Some people do not track these costs, or it really doesn't matter to them..they would just rather raise their own. But so many who don't track, think they can raise replacements cheaper than they can buy them.