People don't get rich if they pay every price. Didn't you learn it from Naida Zamaida in the first pgl quest?
If we can gather iron ore in ARR like sand on a beach, the price would be much lower than 1/10. If it more like Mithryl ore, it would be higher. It is not simple a 1/10 math, you need to think about droprate, too. Everything change. Inclusive the market prices.
And the sellers are not the only one who are greedy. Buyers are greedy and are looking for the cheapest price.
the lowest shield is level 5 (the achievement shield don't count) and it cost 5500 gil from NPC (550 gil in ARR)
