To reduce the amount of money required to open the Malo-Mart in castle town and be able to purchase the magic amor. Donate 1000 rupees to repair the bridge to the west gate to castle town to the goron inside the Malo-Mart in Kakariko Village.

Then talk to the old goron outside the Malo-Mart. He will send you on a quest to deliver some hot spring water to the goron sitting beside the bridge outside the west gate to castle town. To easily complete this quest. Simply walk along the edge of the cliff until you reach the brige. Then smash the barrel of hot spring water on the sitting gorons head.

After you have done this go back to Kakariko Village and talk to the goron collecting donations inside the Malo-Mart. He will have lowered the required amount to 200. After donating 200 rupees a Malo Mart will open in Castle Town and the magic armor will be available to buy.