Material Choice and what I have access to...

[George N. M.]

Welcome aboard from 7500' in SE Wyoming.  Glad to have you.

I'm afraid your question is so basic that I have to recommend that you do some more basic research.  This is like teaching someone who has never seen a car how to drive.

Since you posted this on a knife making thread I assume that you are looking to make a blade.  Probably the best combination of strength, hardness, weight, edge retention, etc.. is a fairly high carbon steel.  You can make a blade out of almost anything but the softer the material the faster the edge will dull.  Copper will sharpen up but will dull quickly.  Obsidian will give you an extremely sharp edge but because it is brittle it will also dull fairly fast in use.

Also, if you post your general location in your profile we can give you better answers.  A lot of answers are dependent on geography.

Also, 'cheap" is relative.  You can make some oretty good blades from scrap steel at 20-25 US cents/pound but any give piece of scrap is an unknown quanity and quality until you experiment with it, particularly for heat treating.

"By hammer and hand all arts do stand."

[Frosty]

Cheap. Light. Strong. Pick two.

Frosty The Lucky.

[ThomasPowers]

Yup more details are necessary; do you need to work it with primitive tooling can you use fancy equipment?  What is it going to be used for?  

[anvil]

I highly recommend Unobtainableium. And if you know where to dig up some good round tuit, it will be right beside it.