After playing around a bit with the plasma cutter, I've had another idea. I acknowledge up front that this is a dangerous thing!
The plasma cutter is way cool ... but not exactly inexpensive, especially to be able to cut anything very thick. O/A is considerably cheaper, at least as far as the basic equipment goes ... I don't know how consumables compare.
Would there be some way to combine the best of both? In O/A, the actual cutting is done by the oxygen, right? The acetylene just heats the steel up to the point where it will burn. Would it be possible to use something like the old carbon arc torch to heat up the steel, and then feed a jet of oxygen to do the cutting? This would require a much simpler and cheaper power supply than a plasma cutter (basically just a CC welder -- and IIRC, AC might actually be better than DC), but should allow cutting as thick a cross section as an O/A torch.
Of course, it may be that such an approach would simply result in the rapid burning of the carbon arc torch rod! On the other hand, if someone gives it a try and it turns out great, let me know. I'm not available to take any of the risks for development, but I'll be happy to participate in receiving royalty checks ...