The following procedure can be performed to get 800 Zenny easily. Have 2 'Kelbi Horns' in your item pouch and then go and talk to the 'Guild Sweetheart' at Moga Village. Then choose the Low Lv one star 'Prescription Pick-up' gathering quest and deliver the two 'Kelbi Horns' immediately to complete the quest. Now take the two 'Kelbi Horns' from the reward box and sell/collect the rest of the items. This process can be repeated until you have the desired amount of Zenny.