I remember the long thread on Budget Paint Jobs, but don't remember any metallic colors. Is there a silver metallic paint that can be used?

I don't think you can roll anything metallic, you'll see the roller lines and it'll look terrible.

I did the roller paint job though on a 81 Oldsmobile I had that I think turned out great.

Not a chance on metallic. Guys have trouble spraying metallic let alone rolling it. Can you say tiger stripes?

Metallics are tricky.
I was told that you cannot color sand the single stage metallic because it disrupts the flakes in the paint. There are 2 ways to get a good metallic paint job:
1) Be a good painter with single stage so you don't have to sand and buff it afterwards.
2) Spray it in base coat/clear coat, then sand and buff the clear.

Looking around the web, I see that Rustoleun makes silver paint that has been rolled on. Pictures aren't very clear, lots of poor lighting. There are reports that coverage is poor, one guy reports nine coats. I wonder how much he thinned it.

I don't know what your circumstances are, but the cheap paint thread premise is that you trade a lot of effort and time for money. The cost is low, but it take a lot of time to prep, requires a lot more labor to lay on the paint, more time to work the surface between layers and the final result is not as long-lasting.
If you can spend a bit more, you could purchase a cheap siphon or HLVP gun, borrow or rent a compressor and shoot the same cheap paint for a metallic.
For double or triple, you can purchase a gun and some better paint and get better results that last longer.
http://www.autopaint18.com/html/paint_kits.html