I'm not too sure. It all depends on where the parts can be had for a descent price and who will be doing some of the work for you. Like bending, welding, etc. Nothing major but some parts will be needing workshop assistance.
I don't want to give any false numbers here but if you post your questions directly to Cody in his forum on the HBS board, you will definately get an answer. ;D
As a matter of fact there was an estimate posted in his forum some time ago about the cost that would require for the project. Check it out.
If you want to start light there is a very good hand held stabilizer plan in the 'tips' section on HBS that is very similar to the Glidecam 4000 model.