Add $ or anything else to beginning of UITextField. The following will prepend a $ when the user types in a textfield and have it deleted when the user deletes their last character

prepend UITextField

func setUpPriceTextField() {

  priceTextField.delegate = self
  priceTextField.addTarget(self, action: #selector(textFieldDidChange), forControlEvents: .EditingChanged)
}


// MARK: UITextFieldDelegate

func textFieldDidBeginEditing(textField: UITextField) {

  if textField.text == "$0" {
    textField.text = "$"
    }
}

func textFieldDidChange(textField: UITextField){

  guard let text = textField.text else { return }
  
  if text.removeCharactersInString("$").isEmpty {
    textField.text = ""
  }
  if !text.hasPrefix("$") {
    textField.text = "$" + text
  }
}

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {

  guard let text = textField.text else { return true }
  
  let currentCharacterCount = text.removeCharactersInString("$").characters.count
  let newLength = currentCharacterCount + string.characters.count - range.length
  
  if string.containsOnlyCharactersInString("$0123456789") &&  newLength <= 3 {
    return true
  }
  
  return false
}