The base model comes with anything you'd need for stairs. The animal model has an extra head with a spinning brush to help with animal hair. We don't have that feature, but have never had any trouble getting anything up without it. The handle is attached to the hose, and it just unclips and will stretch the length of a regular staircase with no problem, so you can leave the vacuum at the bottom and do the whole thing - very nice.
We got ours on-line, and that's how I've found the best prices. They also carry them at Linens n' Things, but not always the base model. Usually somewhere between $400-$550 depending on the model, but no bags or filters to buy ever, so that helps. It's bagless and you just rinse the filters. And, BTW, you can always buy the attachments later if you decide you need them, although they may not be color-coordinated.
Man, I sound like I sell these, but really, I just like mine.