Shopify: Is it possible to update the price of a product at checkout in the liquid template?

Question

If a buyer purchases an item from a Shopify store, we would like to customise the system such that the buyer can select another product from a specific collection in the same store for free with that purchase i.e. buy a premium dvd and receive another dvd for free (where the free dvd must be choosen from a specific collection).

Any suggestions on how best to achieve this?

Would it be possible to edit (hack) the theme's cart template to set the price to zero for the second free item added to the cart if it is in the specific "free" collection?

Answer 1

You can create discount codes that can be applied to a single item in a collection. You can simply set the discount for that item to be 100% off.

Answer 2

If you iterate through a cart and find a "premium" product in it with no "free" upsell product, you would render the collection "free stuff" for the customer, and they could pick from that collection. The products in the Free collection are indeed free.

And if you render a cart with an item from the Free collection and NO Premium item is in the cart, you probably want to disable checkout.

Would that be "good enough"?