I can see why they sell quickly.  Nice work!

 The largest would be about a foot square.  Some barks have a thick outer pulp and a stringy inner bark, others have a very thin outer pulp and a stringy inner pulp, if the outer pulp is too thick it will crack when you bend it, which is o.k. as long as you make cuts through the outer bark so it will crack along them and the inner bark holds it together.  Some of them are made this way, other barks that have a thin pulp will bend without cracking so I make my cuts on the inner bark, very very shallow cuts and bend it along those cuts and the outside is completely intact, I do prefer this method.

  I sell them $20 for the smallest, $30 for the middle size and $40 for the largest, I tend to sell the $30 ones most often.