I think we are talking about different phases of "assembly".
If it is just a bolt together and paint kit, then yea, something less than 50% off for sure.
When I say 50%+, that is for FULL assembly. IE: just shipping the parts as they drop off the saw/press/brake or whatever. With all the jigging, fit-up, and welding being done by the buyer. FULL assembly including the fitting and welding, yes I believe it is 50% or more of the product.
Their new blade weighs in the 465lbs for a 6' model. Around here, new steel (depending on what it is) runs in the 50-60 cents per pound ballpark. So thats about $250-$300 worth of steel. Add some hardware.....The blade sells for $1150. So I would venture a guess that they are getting $700-$800 to cut, shape, fit, weld, and paint the blade. With a kit, all they have left is cutting the parts and rolling the blade. With the right equipment (I am sure they have) that is the easiest parts of the above. The welding and fitting is the hardest and most time consuming part. And for a proper paint job, that is also time consuming and good paint aint cheap either.
So my conclusion, For their $1150 blade, IF I have to do all the welding and fitting and painting and final assembly, I wouldnt want to spend more than about 50%
But if everything is already welded, and it just needs some bolting together and a paint job, then yea, maybe a 25% discount or so.