Do you need widget or shortcode for exchange rates? I needed a good one for myself but i didnt like what wordpress community currently have. I wrote an exchange rate widget and shortcode plugin for WordPress that supports MultiSite.
Its connecting to http://www.ecb.europa.eu 1 time in a day and saves exchange rates to wp_sitemeta if its multisite install (saves to wp_options if single install). So if you have a multisite install that contains lots of blogs, multisite will connect to bank website only 1 time in a day.
You can select which currencies you want to use from 35 different currency option ( those options directly saves to wp_options so every blog have its own). And with shortcode, you can change product prices to different currencies if you want.
Ask me your questions about this plugin in this topic. And please dont forget to "Say thanks to this user! " from topic head :wink: