I am wondering if it would be possible to build a small servo assisted steadicam for a HDSLR for around $200.

A rough bill of materials looks like this:

3 x high torque RC servos ~ $60
1 x wii motion plus (mems gyros) ~ $20
1 x arduino due ~ $20
metal hardware plus
bearings cage and mounts ~ $100

while researching this concept looks like I'm not the only one with this idea, although mine will be microcontroller based (Kalman Filter)


YouTube - Handheld, multi-axis camera stabilization device utilizing MEMS gyro sensors (http://www.youtube.com/watch?v=ewK7NkcCFCk)

If you haven't already, check out the home built stabilizer forum:
Welcome to HBS! (http://homebuiltstabilizers.com/index.html)

Interesting but I think you will want some 1/4scale r/c servos and run them at 6 volts to get the torque and speed needed for your idea. I have a lot of experience with r/c stuff and the servos you will find for $20 are the cheapo ones. I wouldn't use them in any of my aircraft or helis and certainly not trust them holding my 7D.
I'll see if I can come up with a list of ones suitable for you.
I'd love to see one of these stabilizers come to market! Especially near the price point you mention.
When I get more "tinker" time I will be working on a remote follow focus for dslrs using r/c components.

I am at looking at cheap parts at the moment to see if I can get a working prototype together. As far as servos SpringRC 180 oz look suitable for the prototype, although I am expecting noise to be an issue.

As for the rig size think about something like a 550D in a cage about the size of a ViewFactor cage, maybe a bit bigger.

I am using Trex heli bearing blocks and shafts etc to keep the size down

When I get more "tinker" time I will be working on a remote follow focus for dslrs using r/c components.
Let me know if there's anything I can do to help. For example, I've written code for a PIC chip.

cool!
I will definitely look you up when that moves on to my workbench!
Could be a while though...darn clients! HaHa!