Do you need to braze or weld the stuff? Aluminum can be welded especially if you keep it all to the same alloy, it's easy to machine, and you are probably going to paint it anyway. It is also way cheaper than everything but cold rolled steel.
What parts are you going to make? The amount of material and the shapes you need to make might very well be the needed thoughts behind the material to use.
I would probably go with aluminum in 6061 and then either anodize or have it nickel plated. Since I always buy in small sizes for specific projects, I use http://www.onlinemetals.com who will sell stuff buy the foot, they have just about every material you might want to try and prices so you can compare. But as I said you kind of need to know what the parts need to look like before you can chose a material.