I'm confused, what was this page exactly? Like if an item said "~3" next to it, that means... what exactly?
NC trading is a funny thing. The "value" of an item is determined by its supply and demand; if it's rare, if it's old, and so on. You wouldn't necessarily want to trade for items of unequal value, and so a standard is used: Gift Box Capsules, or GBCs.
Cheapie items may go for 2:1, so 2 items per 1 GBC. The most expensive ones are upwards of 100 GBCs per 1 item.
Keep in mind that to send each item, you need a box. You get some from daily spins, but if you are hardcore into NC trading, it's not enough; you need GBCs for those sweet, sweet boxes. Obviously, it wouldn't be very economical to have to send tens of boxes of GBCs, so you might instead want to trade something of similar value in 1 or 2 boxes.