Plugin displays in the Woocommerce cart the amount left to gain free shipping. If the minimum amount is reached, the text disappears.
Woocommerce Free Shipping Remaining Cost adds a functionality to Woocommerce plugin that displays in the cart how much money more user should spend to gain free shipping (if the free shipping min amount option is active).
This plugin requires Woocommerce.
Live demo link: http://demo.borbis.com/woocommerce_free_shipping_remaining_cost/