Real time metal prices and conversion fro USD to MXN using BeautifulSoup updated version
I think it would be better to handle the API stuff to convert prices using a Python package like CurrencyConverter.
The site that you are using currently might be down some day or may blacklist your IP because of the many requests that your code is making to convert the prices.
Also, your code seems to be better converted to a Scrapy project if you are interested in web scraping. Scrapy Tutorial by ScrappingHub