I think $70K for a hair stylist is absurd but if you've seen the dude's apartment, I mean...yeah whatever floats his boat. Donald Trump is a pop culture icon for his extravagant lifestyle. He's mentioned in songs, had a board game and a TV show because of who he is. His entire "brand" is built on displays of opulent wealth, while enjoying many things that are blue collar Americana (McDonald's, diet coke, WWE, sports).
A bartender becoming a congresswoman and immediately becoming a "sell-out" is a unique criticism (right or wrong). I believe a lot of the criticism related to her conduct is tied to her change in behavior and attitudes towards some of the finer things in life upon getting to congress.
She went from being a champion of the poor and what not, to living in a pretty trendy and expensive part of DC, started wearing expensive clothes, spending as much on one haircut as I will spend in 3 years of Manhattan haircuts during school (yes I'm aware women's haircuts are more expensive). Instead of her owning the fact that she had moved to a nice, new, upscale part of DC for convenience or safety or something, she indicated at the time that her luxury apartment should be the new standard for basic housing for Americans.
In short, the criticism of her will be tied to her sudden approval of the finer things in life as soon as she had the income to do so.
I'd look at it in a sorta similar way to the criticism of Bernie Sanders. Dude owns three homes. People will rag on you for being a grifter when you don't practice what you preach or you change your standards of what sort of wealth/income/behavior is acceptable to conveniently exclude yourself from that criticism.
TL;DR version: its not about the amount spent on hair lol, its about the individual's message and how their behavior complies with it.
Donald is a hypocrite on many things, but him spending some ridiculous amount on his ridiculous hair is perfectly aligned with him and his brand (for better or for worse).