36h Velocity Dyads laced to any of the Shimano hubs would be a great affordable wheelset. You could save even more by using a Sun CR18 laced to any Shimano hub you like. The reason I suggest Shimano hubs is they are incredibly durable for the cost. I would really push for 36h and quality DT or Wheelsmith spokes built by someone who knows how to build a wheel. Either of the above should be good for many many miles of rough roads and cross conditions.