Having worked on 3 continents, I've found that it's a matter of finding the right suppliers; I always make friends with local professionals, and they tell me where to go.
Sometimes you need a commercial account, but usually there's somewhere that offers real prices to walk-in customers.
Plumbing fittings of all sorts have massive markups, and huge room for discounting. As someone said, you have to watch those prices. When you buy 1 or 2 items, you hardly notice; but when you build an irrigation system or plumb a house, then you do.
Wiring and infrastructure material too. Often the book retail rate is 600% of the wholesale rate, what I call "government" price. Contractors can charge the high rate and point at the book, but the educated buyer doesn't pay that. Automated manufacture has reduced the wholesale prices and boosted the quality of a lot of things that used to be expensive.
Raw steel is just really cheap, and there are variations in quality but it's almost always in the physical shape [straightness], not the material.
You pay for stocking, delivering, cutting, and billing.