Hi Mariana E,
In Argentina we don´t use the word "prestador" for "lender"; the correct translation is "prestamista, organismo de crédito (like the IMF) or banco comercial" depending on the context.
As the definition of usury is "the activity of lending someone money with the agreement that they will pay back a very much larger amount of money later", I don´t think the term "usurer" is associated with "lender".
I hope it will help!
Piru