For the uninitiated (or frat-avoidant), here's how it works: ladies drink free. Or party free. In either case, there is a standard fee for drinks or cover, and while fellas have to pay it, "ladies" do not. The reasoning behind this is pretty simple. If ladies don't have to pay, they are more likely to come to the party. If there are ladies at the party, men will come to the party. Men are paying for booze/music/party atmosphere, but they are mostly just paying for access to "the ladies." If this were not the case, and the men were just paying for the trappings of the party, then women would be paying too. Women are given a discount simply for attending the party, and men have to pay a price to access the ladies in attendance. If there is a situation with further commodifies women, I have yet to encounter it.
Imagine a hypothetical party at which "ladies drink free." For numerical ease, we'll make $10 the standard price for men. Following the initial "ladies-drink-free-because-men-pay-to-access-them" logic, there are all sorts of addenda that can be made to this pricing scheme. I have made this handy table. Frat brothers of the world, feel free to implement this at your next shindig:
Hope everyone finds this helpful!