I keep my own replacements, I like knowing their history, everything including gestation times is hereditary, and I know that some will always calf 4 days early, and some a week late. Pretty much all my replacements are halter broke, or at least not freakshows if i'd try, and they're all milkable as well... that goes a long way in making calving time less stressful. This year I'm only keeping 2 out of 7 heifers, and I've had 15 bull calves, usually I keep 3 or 4 as they do better in a bigger group.
I think the 5 years to break-even is about right regardless of whether they're purchased or raised, it's one of the reasons I don't cull old cows just for being old. If a cow does well up to 10 years, I'm going to want to get some heifers from her, so if I want 3 more, odd are she's going to have to get to 16 for that to happen. I think the 5 years to break even would prove true if you had to replace all your herd at that age... First calf or even 2 are always going to be a bit smaller, so only by the 3rd does the cow really start to work.
I keep costs down pretty well, but hay prices are pretty high in my area at $8/ 80 lb bale.., or $200/ton.. I feed my replacements well, so lets say 30 lb/day for a year (bred heifer in fall) is bang on $1100 in feed, so add the cost of the calf to that at about $1000 around here, you're at about $2100. I could buy cheaper hay, but it'll reflect in how they grow. My heifers are usually around 900-1000 lb at breeding, 12-1300 at first calf. I don't retain heifers that are under 600lb @205 days, and most are about 675... I've had some 750's but usually they didn't have the build I was looking for and passed on them too