In reality, the price of the SM58 has really dropped.
If you looked at the price in 1975, it was $101. Today, it's still $100. Considering that you are talking about a time span of 48 years, that's pretty incredible. The 545 Unidyne (predecessor to the SM57) was $69. By 1982, list price of the SM58 had gone up to $175. So in the past 40 years, the price has dropped by 45% not taking into account any inflation! At some point, you start to lose money. Maybe the Mexican workers make more than the Chinese workers. Who knows? Any way you look at it $100 for a good solid mic is cheap these days.
$100 is 2 tanks of gas today!