All that follows is predicated on the assumption that the bridge is stable, since the OP didn’t specify its construction. You’d need lots of support to keep the smaller widths from bouncing and flexing like a trampoline. If we’re talking about bouncing bridges…no. Well, maybe the 4’ one, but I’d want to watch it for a while first.
I routinely cross short distances on 4" beams, but not over dangerous heights, and not 60’ spans. I would be concerned about fatigue, wind effects, and possibly vertigo, so I’d be dubious about walking the 6" version over that distance. I would want to advance sideways by shuffling my feet, rather than one foot in front of the other; it’s more stable, but also slower and more tiring. One leg tremor or cramp away from death is not a place I want to be. If it were “Cross the bridge or stay here and die”, I’d head right out and probably be okay, but I’m not risking it for cash.
The 1’ bridge is not actually much better in this regard–it’s still not wide enough for me to abandon the shuffle transit. If I’m already giving up $900K, I’ll give up another $60K to switch modes.
The 2’ bridge is wide enough to walk one foot in front of the other, with enough spread for some balance. Also, it’s probably wide enough to take a knee to rest or regain my stability, if necessary. Sitting here at my ease, I picked it. I might reconsider on actually looking down at the drop, though.
For the sake of a complete analysis, the 3’ and 4’ bridges are practically the same as walking on flat ground, as long as you don’t look off the sides.