What is the most cost effective way to build a rain screen wall assembly?

We are trying to make the most cost effective eco wall for our projects here in zone 6 in Grand Traverse County, Michigan.  We are recycling buildings and reconstructing them for affordable housing.  I'm a real fan of the rainscreen wall as it really lets us be creative with the exterior cladding materials.  With the cost of materials all over the place lately we are going to do a lot of research on this to make the right choices. 

Typically we have been using from interior to exterior... drywall 2x6 stud wall 24" o.c. w/1.5" closed cell and 4" open cell insulation (for sealing and cost reasons) 7/16" sheathing, tyvek house wrap, metal siding.  Would like to do more of an  assembly like this and would like your opinion on both or better options... reclaimed barn wood over 1/4" drywall, 2x4 stud wall 24" o.c. w/ rockwool insulation in cavity, 7/16" sheathing, 2" EPS Rigid Insulation, water-resistive barriers (WRB), vertical firring strips 24" o.c., 1/8" gapped 1"x6" reclaimed barn wood horizontal cladding.  We would really like to make recycled material we have available to us usable with the right assembly to ensure no future issues with water damage to the interior cavity of the wall system.  Thanks!