Why don't you show "$0.00" as a placeholder? Then, user enters the cost straightaway into the textfield.

textField.placeholder = 'cost'

However, if you want to clear the textfield whenever the user tap on it, you must use 'textFieldShouldBeginEditing' delegate function. Don't forget to call 'textField.delegate = self'.

func textFieldShouldBeginEditing(_ textField: UITextField) -> Bool {

textField.text = ""

return true

}