I bought an articulated microscope arm a few years ago, but I was never really happy with it. The arm was too wobbly - the parts did not fit exactly and had too much play. While preparing I had to avoid bumping into the microscope, otherwise the microscope started to swing up and down.
Now I have built myself a very sturdy double arm boom stand.
I used two 16mm ball-type linear bearings and two solid linear motion shafts (16mm diameter, 80cm long). The end pieces and the support are made of aluminium - I had the holes drilled by a local company for 15 dollars. Together, it cost me about $ 90.
Works fine!
You can buy double-arm boom stands for about $ 200, but the arms are too short for my purposes.