This example begins in past tense, so I’m keeping that throughout.
Her job was to walk the Earth and seek out other survivors of the old world like herself and hand them over to the boss for a price. A modern-day bounty hunter. The males fetched a higher price than the females. She didn’t know why, and she didn’t know what happened to them once they were handed over. She did this only to stay alive.
If you set aside part of a sentence with dashes, you need a dash on each side, not one dash and one comma. Likewise, if you use commas or parentheses or whatever, they need to match.
The sentence fragment A modern-day bounty hunter jars badly, and not because it is a fragment. I’d recommend getting rid of it or at least replacing the modern-day part.