Eeek? Home Depot? They are about 6x more expensive than buying from a
real metal dealer.

You didn't say where you live. If you are on the Peninsula, Metal
Supermarket in Redwood City is a lot cheaper than Allan Steel. Also,
Ron at Metal Supermarket has reasonable prices on cutoffs ($3.99/lb for
stainless and $2.99/lb for brass) and is a lot nicer to deal with than
Allan Steel.

Also, there is Allied Iron in Belmont that carries steel, aluminum, and
brass.

If you want Aluminum for casting, Pyro Minerals in Oakland sells ingots
of A356 for about $2.50/lb. After finding Pyro, I gave up scavenging
wheelium, pistonium, and diskdrivium.

-Aaron