I purchased 2 runners at Christmas Tree Shop for $14.99 each. That was enough to cover our 5 stairs. It is an indoor/outdoor rug so hopefully it will hold up to our crazy house.
Please excuse the bad picture I snapped quickly with my phone. Sheesh, I really need to get better about taking "during" pictures. We used clamps to hold the carpet in place as we stapled. It took us less than a 1/2 hour to install the runner. We made sure to have the finished edge under the first step and at the bottom of the bottom step's riser. We joined the two runners underneath one of the treads.
The project was fast, easy and affordable and I am glad we finally got around to getting it done.