David didn't say it directly so I will.
If you don't have a 4"-4&1/2"-or some such small grinder spend your money on that. Then cut and grind your tools from locally available hammers. A geologists hammer may be a pick, -polish the end for a fair sheet metal pick or a long cross pien geo hammer, again polish the end for a metal working tool. Heavy machinists Ball-pien hammers can be re-shaped to become useful in sheet metal, and in the shaping-reshaping and again shaping you'll come to understand the why-s of the hammers shape more than you get from a set.
You'll start by gathering your metal from where you can DO NOT CUT A BARREL OF UNKNOWN CONTENTS. You'll use the grinder to cut, shape, and smooth your projects. later to clean up your welds.
Here is a page with a few grinders on it for example, I make no recommendations, I tend to get mine from tool resellers (pawn shops) but often have to rebuild them I've no preference short of the Metabo which is more expensive than I'll buy new.
http://www.sears.com/tools-corded-ha...ack+%26+Decker
Go to the shops you well eventually buy material and tools from, study what they have, welding suppliers, metal suppliers, jewelry supply stores, mining suppliers, blacksmith suppliers, and "That guy down the street".
Read
To your question "bare essential tools" --two rocks-- you're beyond that already? You have hammers around you. You'll find some to sharp on the edge and leave little crescent marks, some to rough leave recognizeable "That hammer" marks, and failings in ever hammer you pick upso try another one or reshape the one you have. (wet and dry sandpaper you can get so fine the scratches disappear.)