Free shipping over amount is one of the basic functions of the Flexible Shipping plugin.
Free Shipping value
To set free shipping over amount just enter the free shipping value in the shipping method settings.
If the cart value exceed this value, the plugin will automatically offer free shipping. This feature overwrites all rules based on price, so they will work only up to the free shipping value.
Free Shipping label
You can also set a Free Shipping label that will be displayed with the free shipping option. To do that, just enter your label inside Free Shipping Label field.
If you set Free Shipping value as 100 and Free Shipping Label as Free shipping over amount, the shipping method for ther order which is $100 or higher will look like this: