After using a cheap folding chair as a computer chair for about a year, I finally decided it was time to upgrade. I've bought executive computer chairs before, but have always been annoyed with their poor quality and ridiculous pricing. A few pieces of foam wrapped in vinyl on a cheap plastic base should not cost $200 to $400 in any currency.
Instead, I went to a local wrecking yard and picked up an 8-way power leather seat from a Volvo sedan for fifteen dollars.
I sourced a base with five casters and height adjustment from an old chair around the house.
I then bought a piece of plywood to join the base to the rails of the chair.
The chair's rails are not the same on both sides, so mounting the wood was a bit of a challenge. The wood ended up being a bit warped, but using some washers as spacers made the chair sit level on the base again.
One challenge with the fitting of the chair to the base was finding the correct place to mount it. If it was mounted too far forward or back, the chair could fall over.
The correct location was determined mostly by trial and error. The chair itself is actually very heavy, so when no one is sitting on it, it is slightly closer to falling backward than forward. As soon as someone is sitting on it, the balance becomes pretty much perfect. As of this writing, I have been using it for about six weeks with no threat of falling, even when leaning forward or back on it.
The chair could be made to look good fairly easily. The only really odd looking parts are below the seat bottom. Painting the wood a dark colour or attaching cloth to it could make the chair look very nice overall. I spent no time on aesthetics, and it looks alright anyways.
The chair is very comfortable to sit on, putting most "real" computer chairs to shame. It even has adjustable lower back support. It was cheap to make and should last a very long time. The project was a complete success by every measure.