"Going from a 6 to a 6.5... represents an 8.3 percent increase in attractiveness, while going from a 6.5 to a 7 makes for a still-desirable 7.7 percent leap. Even if one had to spend a corresponding percentage of one’s disposable income, it might make sense. (Of course, results may vary; my own advance up the scale has been less dramatic. The last time I got catcalled, the guy yelled, 'Girl, you look just like a second-grade teacher!' Disconcerting largely because it's true.)"
From "I Spent $11,537 Becoming a Blonde" by Catherine Baab-Muguira in New York Magazine.