A pretty simple, but seemingly important feature; an additional gauge/meter option (like the one that measures 'amount of items' added to basket - it's a progress bar) that allows the customer to see how much more they need to spend in order to trigger the discount incentive with the build-a-box subscription feature. As it stands, the customer wouldn't even be aware of the discount benefits until they reach the checkout page. Conversions can definitely be increased by placing it on the product selection page.

Would be an incredibly useful feature.

P.S. more customisation options for the product selection page for build-a-box would be awesome too. It's rather 1 dimensional at the moment.