Neat barn, not sure where you are located, but one way would be to spray foam the inside of the exterior barn boards and then vapour barrier and cover the inside with whatever you choose, probably at least half inch plywood considering the span of the studs.
I do not remember seeing a particular thread on what is best to put on the interior walls of a garage. The frame will be 2 X 6 studs with ceiling trusses. The cheapest is probably drywall, but it may not be the best. What have you done? How has it lasted?