This extension lets you see how long it would take you to earn a certain amount of money when hovering over prices while browsing with a small tooltip.
TimePrices supports 4 currencies at the moment: USD, EUR, GBP and JPY.
You can configure your income in the settings, and blacklist or whitelist specific websites for the extension to run on.
TimePrices is free and open-source. Feel free to report issues or fork your own copy.