No, they are not. But they are marginal.
This is an artificial example, very specific to me. I make two flavors of fuel blocks based on closest available ice. My blueprints are maxed at 10 ME. Blocks are made in rigged but not maxed facility. If I bought all required raw materials at Jita sell price I might make an extremely thin margin on sale of blocks. But even with maxed trader, sales taxes likely make it a thin loss. That’s why I start with my own ice, as primary producer, to reduce input costs. Not using the term here in its proper sense of opportunity costs, simply input raw material costs.
In practice, it depends if you can actually sell those inputs. The benchmark price for inputs is usually the Jita buy/sell prices. But, if you can’t physically get there to sell, then for me, in practice, I might not get sales at all. That means the opportunity cost for me is actually zero. Technically, there is a sale option, but in practice it just isn’t there. Not in my two closest hubs.
Can’t speak to the cause and effect here but ease of sale is certainly one reason I make fuel blocks. Even though compressed ice would probably be my preferred market. The problem is, I have to find that market. My local trade hubs both deal in the “wrong” flavor of ice compared with the main one I mine. And I typically get much quicker sales if I take my higher volumes of compressed elsewhere. Which takes time. Dealing in the “wrong” fuel block by comparison is much less of an issue, but it is still an issue. (This is because fuel blocks are also used as inputs, not just for fuel, so people will still pick and choose by preference not just on price).
You can, with good reprocessing skills and maxed athanor (got both) generate more inputs for sale from processing ice. I do that processing, but compared with selling compressed ice, both the increase in volume haulage and the low unit price(s) further complicates the time-to-market dynamic - both in terms of time to get there and time for me to sell. So, again, selling compressed would be preferred for me, if I could do it locally.
This is where it gets really complicated. If you mine and process the ice, as I do, then you would think fuel blocks would be more profitable than selling either the ice or its components. They are not. This based on price of inputs I have to buy. (And assuming I would be prepared to long haul to market to sell them instead.) However. You do end up with spare inputs from processing ice because blueprints and ice composition are not in balance. (Strontium clathrates are your limiting input from ice). Now, if you value-add to those spare inputs, you can then make more money than just selling the ice components alone. But to do that… you need even more inputs. And keeping track as to how much money you are making from selling several products now - compared with the combined opportunity costs - is where EvE goes from game to job!
My reasoning for doing value-adding though, apart from excuse to put up a structure and play with it, is that if you look at those same hubs where I can’t guarantee to sell at Jita prices, I can get some inputs at much less than Jita buy. So, with patience and permanent buy orders, the dynamic changes again, and fuel blocks are back in my favor. Plus, I make some fuel blocks for myself, at cheaper prices than I can buy. But whether any of that is ever better than opportunity costs overall (depending on what discounted values you use for input material costs) … who knows ?!