I've used the Steadicam Merlin before. It's a true PITA to setup, as there's no published settings for Pentax gear on the cookbook website, but once you figure out the proper balance, the video looks like like the camera is floating on air. Very pricey though.
The Flycam Nano looks be a cheaper option, but you'll have the same problem of figuring out the balance settings on your own.
Here's a video I took that demonstrates what I was able to get with a Steadicam Merlin and non-optimal settings (had to come up with the settings on the fly):