DropDown在mvc中更改时，从模型设置TextBox值

I've got a ViewModel called Bill who has a list of a model called Product, the Index view that use Bill ViewModel has a DropDown with the names of the products and a textbox where I want to set the product's price (located into the product list) into the textbox depending on the product selected in the dropdownlist.I've got a ViewModel called Bill who has a list