In reply to your first comment, more things go wrong with the hubs than people think. Now I am not saying that every hub is bad, BUT, when the bearing fails, it usually allows the hub to move beyond the normal position (this is what you feel when you wiggle the tire and feel the movement. It is the hub and inner race of the bearing moving together) When the hub is allowed to move off true, then it begins to apply unneeded pressure on the seal that it rides on. This can quickly wear the rubber off, and allow the sealing surface of the hub to rub against the metal of the seal. Once this happens the hub is damaged. You can still press out the old hub, replace the bearing and install a new seal, then get the hub pressed back in, but if the hub flange has been damaged, it usually does not take much more than a few thousand miles or even less before the seal fails and allows dirt and water to get into the bearing. I have seen it happen many, many times over the past several years of doing this.
To reply further, You know the exact parts, as I quote them in my list. I use factory Toyota o-rings, and mounting bolts on the 4WD and 2WD assemblies. As for the bearings, I purchase in bulk from Moog (Which make your SKF bearings) as well as direct from Koyo/Timken. I do not use the cheap e-bay bearings. I ONLY use bearings manufactured in Japan. The housings are assembled new, with the bearings already pressed inside, as pictured. The seal between the hub and bearing/hub unit is Timken, which again are made by their parent company, Koyo. When it comes to the hubs themselves, I use Dorman hubs for the 4X4 versions, just like everyone else, and for the 4X2 versions I use only Toyota 2wd hubs and backing nut.
Everything is high quality, and properly assembled. I have been doing this for 2 years now. So EVERY single part is brand new. Nothing is reused. The third point, as mentioned, is that you are paying for the convenience. As it sits now you have to go to the parts store, get the bearing and seal. Then you have to get a ride to take your assembly down to a shop to get the old assembly pressed apart, and the replacement part pressed in (Not everyone owns a press capable of doing this) After that, you then get a ride home and put the truck back together. My assemblies are ready to install. You simply unbolt yours, bolt mine in, and go! Usually less than 30 minutes per side and you are done! It is the convenience that you are paying for. You COULD drive all the way down to the grocery store to buy beer for a lower price. Instead most people go to the local corner store because it is convenient. They know that they pay more, but then again, they are paying for the convenience.
By the way, I challenge someone to find THIS quality of an assembly being sold for the prices I do.