Having had a wife and two daughters, plus a dad that worked for a dry cleaner, I had some practical knowledge.
There's other things that women pay more for than men, but that was an industry wide standard.
I'm not sure how much it costs them to have their hair trimmed, but a simple trim generally costs more than a guy getting a trim.
When my ex and I first considered getting a divorce, one thing I discovered was that because our oldest girls was 12, it'd cost me an extra $40 a month in child support and would increase more when our younger daughter hit that age. As you pointed out bras, other items pertaining to young women were costly. A boy can get by with a few pairs of slacks, shirts, tees, socks, drawers, as well as gym shorts and a single jock strap. Girls have slacks, jeans, dresses, socks, panties, pantiehose, bras, slips, and usually add make up, hair ties, jewelry, etc. Guys want our girls, daughters and wives, to look their best.
On more than one occasion, I've sprung for a girlfriend's birth control pills.