Another approach could be to break down the various components of supply chain and analyze their costs for each of the compoenents of revenue generations. For. eg you may want to break costs for each product cluster as
1. Inbound costs, which could be further broken down into - Procurement costs/manufacturing costs(in case we make or grow anything on our own), Logistics expenses interms of warehousing and transportation. Another branch would be costs of inefficiency interms of buying low quality goods which leads to rejections or cost of inventory.Then we can further break each component into labour expenses, raw material expense, fuel expenses, cost of equipments etc.
2. In-store costs - We can define cost of handling. FUrther we could highlight cost of inefficiencies in terms of rejections of peroishable items as they were never sold due to poor demand planning.
3. Outbound costs - If they have home delivery option. Key thing to look here is whether they have ecomonies of scale for each outbound delivery they make.
3. Cost of reverse logistics - This traditionally is the biggest burden on any retailer, in case they offer free or subsidized returns.
Look at each of these cost buckets and compare them with the competition.