I like the cutoff fatigue idea. Modern fatigues are made of a rip stop synthetic blend that should wear well.

FWIW, a company called Endura makes some interesting pants specifically for cycling that they call 3/4 Humvee, kind of 3/4 length nylon cargo pants with a lycra crotch panel. You can see them at endura.co.uk. This model is not actually sold in the states, but I emailed the US website and was told they would special order some from UK for $84.95. Still more than I wanted to spend, but less than many similar pants.