180 wheat = about 3 stacks or 1 stack of bread. One stack of bread usually sells for around 100cr. You are correct in this assumption. Couple of things though. You are not taking into consideration the persons time to perform not only the planting and harvesting and trading of all that wheat for 54 picks but the value of the emeralds alone far outweigh the price of 5400cr you are offering for those picks.
54 * 10 emeralds(average cost of a diamond pick via NPC) = 540
540 / 64 = 8.43 stacks of emeralds needed for this trade you are asking for.
This thread I've linked below will give you a good idea what emeralds are worth.
http://www.minerealm.com/community/view ... f=8&t=9886