I don't think people try to trade for an item's original value. I often see shovels going for 1.5 shells each. Just because a shovel costs $50 Gralats doesn't mean someone will want to pay 10 shells for it.
The community creates the economy. I have traded for and obtained a Crimson Blade, currently valued at about 2000 shells ($6000 gralats if trochus), but its original price was $18,000 Gralats.