If you want the "old time" look, give Charles Holland in New Hill a call. He has a circle mill and sells pine for a pretty reasonable amount.
If band mill marks are acceptable, give Jack Murdoch up in Rolesville a call.
I too am about to build a 16'x12' structure and am looking for any cheaper alternatives to plywoods and panels. I also would prefer the wooden plank look. I'll check into these two. Any other good suggestions between Raleigh (my work) to Greensboro (my home)?
*edit*
Greensboro being more ideal as closer to home.
I happen to have about 180 pieces of cedar mill Hardie horizontal siding. I got it for a project that did not get off the ground and would like to see it gone. I will sell at a LOW price