The salaries for public defenders, who are assigned to defendants who cannot afford their own attorney, are paid for by?

The state.

Explanation:

Public defenders are those government lawyers or attorneys who have been assigned/appointed by the courts to the criminals that cannot afford to hire their own lawyers. These government workers are assigned to defend the accused criminals in their court cases so that they can also have a fair trial, free of cost.

While the cost of these defenders are free for the criminals, meaning they don't have to pay them for their service, the defenders are not without salary too. They are provided salary by the state government, who provides them the pay from the state funds. In the United States, it wasn't until 1963 Supreme Court case of Gideon vs. Wainwright that it allows the option of criminals to be provided with legal help for free. Brazil, on the other hand, provides an office for public defenders in both the state and federal levels, thus making it more easier for poor people to get fair trial.