Back to the custom intake material...

I would make mine out of Aluminium because its light, and doesnt warp as much as stainless does when you weld it, but for me mainly it would be becuase it is easier to work with... Be careful with the Aluminium when your handling it cuz its soft and will scratch easy.

Stainless is cool too, I made my exhaust manifold out of it.

When it comes to cost, it dont really matter which way you go cuz both are freakin expensive nowadays.. S/S is more though.

As far as using mild steel.. forget about it, thats just a dumb idea.. all that rust potential to go in you engine.

If your going spend the money or time fabbing it you might as well use the more expensive material becuase the cost of material will be nothing compared to the cost of having someone build it.. and if your doing it yourself you want it to look good right..