This steady cam only needs a few non-printed parts, the rest can be printed. Z rotation is enabled by a 608 ball bearing, while the other two axes are just running on M4 screws.

The design works great - of course, a "pendulum type" steady cam like this one has some drawbacks, but it's still good enough for some really nice action footage!

After designing this, I found one here which is also very simple and cheap and additionally has a very nice design: http://www.thingiverse.com/thing:84142. Maybe I should have searched first ;-)
I really liked MaximFilm's idea of the handles for the threaded rod, so I decided to adopt it and also add one above and below the gimbal.

Anyway, this one is even cheaper. I paid 1 Euro for a 1m M8 rod and about 3 Euros for almost a kilogram of nuts and washers at our local hardware discounter. The most expensive part is the bearing - if you have to buy it. I took mine from an old pair of rollerblades. So, together with approx. 20 meters of PLA, total cost is much less than 10 Euros.

UPDATE: Parts were re-uploaded in the orientation I printed them.

You will need the STLs printed (all of them should print without support besides the GoPro mount) plus:

• one 608 ball bearing
• 9 M8 nuts
• some M8 washers
• an M8 threaded rod, length still tbd - I think it will be around 40 cm
• an M8x100mm screw for the handle
• four M4 x 20 mm screws (you will have to trim them)
• four M4 self-locking nuts
• four M4 washers
• some big washers as a weight (I used 10 with a 13 mm bore, so I used the "Weight tube" printed part to center them)