Free choice or not? Offer monetary compensation to drug-addict women to undergo sterilization

I'm reading the story about this person, Barbara Harris, who founded a charity organization to offer drug addicted women $300 cash if they will undergo sterilization or long-term birth control. This "charity" practice has since started a lot of debate and controversy.
But I have no intention to argue if this is ethical or not, the only thing I want to talk about here, is about an argument the author of the book gave on the perspective of opposer of this practice. "Given her addiction and, in most cases, her poverty, her choice to be sterilized for $300 may not really be free."
You say it's not free choice because they are poor and in addiction? That's just regarding the issue in your own perspective, as middle or upper class of the society, you certainly will feel that selling the right to give birth for $300 is not a free willing choice, but to them this may be a lot of money, could support a woman survive for quite a long time under extreme bad situation. If, say somebody offer you this deal, but not $300, but $3,000,000, which just match your social status, right? You may just need this much money to pay some debt or medicine bill or whatever. Then is it free choice for you to choose to take or refuse? Of course it's free choice, you can refuse or take it, it's all up to you. But if you take it, someone who's richer, say who has $300 billion would consider you as didn't make a choice under free will.
The money benefits the women, in a way you probably can't imagine as a person who doesn't live in poverty yourself. So, false argument.