Minimum spend coupons

[#1]

I want to create a coupon that allows a customer to make a $100 purchase to receive a free item.

I can set up the free product, but i can't set up the $100 minimum spend anywhere. I want the customer to reach this threshold before the item is discounted for them. Is there any way to do this? Maybe a 3rd party plug in or some code you add for me?