You may be able to find some nice, sturdy "29er" rims, too, although a lot of those are 32-hole.
I recently finished a 3+ week tour in Europe (Munich to Barcelona) and I built up a pair of wheels using WTB DX23 rims (32-hole) which were only about $20. We rode lots of rough roads and were on some gravel roads almost every day, too, and the wheels held up great.