As far as I know, Nashbar's dedicated touring frame is aluminum, not steel. They do offer 2 steel MTB frames, one with Reynolds steel, one with high-tensile, the latter being good for a $50 beater/townie frame. The touring frame seems to have gotten good reviews in the forums, although I have not particular experience with it. Steel is the generally accepted tour bike frame material, but aluminum works fine too. It depends on what you're used to and how seriously you plan to tour with it.

As for other places to find cheap touring bikes/frames, there's always craigslist and ebay. If you're not a terribly experienced biker, craigslist may be better because you have more of an opportunity to go see and test ride the bike. I'd look for an older steel Trek or similar bike. They can be had in good condition, complete and probably in need of a tune-up and new tubes/tires for $200-$400 or so. That's where I'd start.