There are many buses that go from Phuket to Krabi town.
I went From Krabi town to Koh Lak changing in Tak Kupa,total cost was 140BHT.Also took taxi once 2200 Bht.
I also heard that a VAN arranged by Krabi Shearton would be 3200 BHT to Phuket/Patong in either direction.