Maybe I'm clinging too tightly to tradition, but if I wanted to build a cheap, tough, weight-weenie wheelset...

I'd start with the 32H/36H VO low-flange hubset, which appears to be the same OEM as the Circus Monkey hubs, but available in 36H rear drilling and nicer finish. Lace it to 24mm carbon tubular rims direct-from-China (several eBay sellers will drill them however you want... where else would one get a 36H carbon tubular rim?) with Sapim Lasers from Dan's Competition.

Those carbon rims are supposedly about 200g (lighter than even the weakest classic alloy pista rims), and I'm guessing they'd build into a pretty strong 36H rear wheel. Glue on some Challenge or Dugast fatties and you're off to the gravel grinder. :-D

Edit: 1100g and about $500, if you believe the mfr specs. About 1850g with skewers and Challenge 30mm tires.