How to model ski rental equipment
Most of that model looks very good to me.
I think the piece you're missing is the concept of a package.
I would make some products packages (or sets) of products.
product
product_id
product_name (could be &quot;diamond package&quot; rather than &quot;ski&quot;)
sale_price (if product available for sale)
is_set (boolean indicator that this is a set, not a single item)
set_detail
set_detail_id (just a serial / autonumber)
set_product_id (references the product_id of the set)
set_item_id (references the product_id of the item within the set, e.g. ski or boot)
With that, I believe the rest of your model, including the complicated pricing, works.