These.
I use a regular saw and never had a problem. On thin metal, I have been known to use a standard saw blade with reasonable results.
Buy a decent circular saw and a metal blade. Unless you cut a shit ton of steel the metal specific ones aren't worth it to me. I use a metal cutting 5" blade in my Porter cable and it eats 5/16" steel for lunch.
These.Everyone said that about the shielding but I didn't notice much of a difference going from a metal cutting saw to the Porter cable. And the Porter cable cut faster and had more power. I suspect it has a higher blade speed. The chips sucked and got everywhere with the metal cutting saw, and all the shielding only served to gather them up and drop them in front of the saw where they totally obscure the line you're trying follow. The Porter cable scatters them a little more but at least they aren't in the way.
The best part is you can buy a new half decent circular saw and a kick ass metal cutting blade for less than the price of a used metal cutting saw. And cut wood with it on the 364 days a year you don't need a metal cutting saw.