I'm really cheap, but even I broke down and bought one... Though I was pretty adept at swinging a hammer with a steel brace at the underside of the crank, it was quite a precarious operation, and I knew I'd inevitably miss one day and damage a lock ring or crank.

Plus, BikesmithDesigns' tool is a pretty impressive hunk of steel - Just having it makes me feel like a better bike mechanic than I actually am.