I am looking to find out which is the cheapest and which is the most expensive way to build a pikler triangle. Option A: baltic birch plywood on the sides and fir for the rungs Option B: baltic birch plywood for the sides and birch for the rungs Option C: eastern pine for all Option D: baltic birch and pine wood Is using pure wood better than plywood for all or it wont really make much of a difference? Thank you!