In the US white women earn $0.77 to the white male dollar. Women of colour, trans women and disabled women earn even less than that.
As for your question, it doesn’t quite work like that. In the United States, the gender pay gap is measured as the ratio of female to male median yearly earnings among full-time, year-round (FTYR) workers. The female-to-male earnings ratio was 0.77 in 2009, meaning that, in 2009, female FTYR workers earned 77% as much as male FTYR workers.*
There are employers that pay men and women different amounts for the exact same position but this only explains a small part of the gender pay gap (partly because there is legislation in place to stop this.) More frequently women earn less than men for doing jobs of equal value. One of the main causes is the way women’s competences are valued compared to men’s. Jobs requiring similar skills, qualifications or experience tend to be poorly paid and undervalued when they are dominated by women rather than by men. For example, the (mainly female) cashiers in a supermarket usually earn less than the (mainly male) employees involved in stacking shelves and other more physical tasks. The gap exists not just because of discrepancies within individual businesses; it’s the product of many complex factors.
Your question is looking at the problem the wrong way round. If the owners of one of these dodgy businesses were in the habit of paying all their women workers less than their male counterparts it would have to be because that business attaches less value to the work of women. So hiring all women would, in their eyes, not be cost effective, because they value that work less anyway.
