The price per pint is roughly 2x what it'd cost in a store, but the milk is fresh, organic, delivered to our door - and very importantly for us - generates very little waste. The empty glass bottles go back with the milkfloat, so we use far less plastic cartons.
You may be 100% correct in this case, but in general, I think this is a very hard thing to discern, especially without a pretty deep analysis.
I'm not saying it is perfect, but I would think that 'price' is highly correlated to efficiency of the product delivery pipeline and efficiency is probably well correlated to 'waste'. The major confounding factors would be understanding what externalities are (or are not) being included into the final price and the distortions introduced administratively by government policies.
So a 2x price factor, to me, is indicative of possible inefficiencies relative to store distributed milk but certainly not definitive.
First, the volumes are much smaller. A large store chain can negotiate prices lower because they will be shifting a lot more product. The effect on unit margins adds up on both sides of the equation.
Second, the cost of labour. A grocery store should have a fairly big figure for units sold per employee. (Not just milk, but everything they sell.)
Third, we are obviously paying for service and convenience. The milk is delivered fresh, early in the morning. We just open the door and get the bottles. The fact that the empty bottles are taken away for no extra effort is an additional convenience factor, but one of the big reasons we originally went for a milkman service.
Number four - the milkman company is a business. They need to make a profit too.
Because the company operates with a dairy, I can probably discount the cost of specific cold chain maintenance. They would be maintaining the equipment and cooling in any case due to the products.
We could get groceries delivered from the shops, but that is still less convenient. The delivery slots are either during the day or in the evening, and we need to be at the door. Delivery is an extra charge, and priced so that it makes economical sense to order a lot more in one batch. This actually adds a disincentive to ordering milk: we enjoy fresh milk, and with longer delivery intervals it sure wouldn't be as fresh when we drink it.
And finally: the amount of plastic waste, even with our reduction tactics, is pretty significant. If we bought our milk from the store, we would need at least one more plastic recycling crate to hold all the milk cartons.