function parsePrice(saleInfo) {
  if (!saleInfo || saleInfo.saleability === 'NOT_FOR_SALE') {
    return null;
  }

  return {
    currency: saleInfo.retailPrice.currencyCode,
    amount: saleInfo.retailPrice.amount,
  };
}
Parse the Google Books price format into a proper object.

@param {object} saleInfo The Google Books price.
@returns The price object.