So the size of an item changes it's price. Does that apply only to the standard quality, or does that change the price of other quality items? The base price of the item is ignored in favor of the item quality price, is the size multiplier only for the base item or also the item quality? So would a Gargantuan Legendary greatsword be the same price as a medium one, 65,000 sp, or is it 8 times as much, so 520,000 sp? I know that it's the same price as a Gargantuan Legendary dagger, which is a bit odd. Unless it's a special material, in which case the bulk dictates price so they'll be quite different. And I'm assuming for the different materials the price multiplier isn't used, and instead we just use the price based on bulk, otherwise things are double counted and a Legendary Gargantuan Adamantine greatsword would be an insane 1,920,000 gp instead of 240,000 gp for a 16 bulk item. And likewise, I'm assuming size doesn't change the price of potency or property runes.
There's a lot of weirdness and unclear writing with the way item prices are now sometimes substitutions and other times multipliers or adders. Like quality and special materials replacing the price, but size multiplying (and the question of just when it multiplies and when it doesn't). I'm helping a friend on a web based tool to automate item price calculations, and we've been running into it a lot. Oddly the simplifications actually have been making some things more complicated. There's less math, but more exceptions.
According to the current rules as I read them, *all* medium Expert standard weapons cost 350 sp, *all* medium Master standard weapons cost 3600 sp, and *all* medium legendary standard weapons cost 65000 sp. Then you adjust for size, so a gargantuan version of each of the about would cost 2800, 520000, and 520000 sp, respectively. I suppose other readings are possible.
I think if you're going to speak of things made with special materials, you should calculate the price for the medium sized item made with that material, and then multiply by the size multiplier.
The price for the magical components of magical items doesn't change, as I read it, based on the size of the item.