There is a local place that will print 1,000 door hangers for about $60. I think that's probably a safe, nonobtrusive way to get the word out. My plan is to hang them on doors during the day when no one is home, just to plant a seed. Then maybe canvass that neighborhood 3 days later.
Thats a good price. But think about this. How often does "non obtrusive" actually get the word out? Door hangers are a good supplement to other forms of marketing but you want people to physically have to pick up your advertisement or take a second look at it.
With all that said, the only difference in a door hanger and a rock flyer is the product placement. People get dozens of door hangers a year from contractors. I personally want to be the only one putting a flyer in their driveway. They'll remember me.