-information from March 2016-
There are two ways to get to Tonsai from Koh Yao Noi. And as always it depends on your budget.
# option 1
You can take a speed boat from Manoh Pier (in the south of Koh Yao Noi) directly to Ao Nang, followed by a longtail boat to Tonsai. There is only one speed boat a day leaving Manoh Pier at 15:30. It will cost you 600 THB for the Speed boat + 100 THB for the taxi to Manoh Pier (as you probably stay in the Tha Khao Pier area) and another 100 THB for the longtail boat to Tonsai.
Total: 800 THB
# option 2
Take a longtail boat from Tha Khao Pier to Thalen Pier, a bus to Krabi and then a bus to Ao Nang, followed by longtail boat to Tonsai. There are several longtail boats a day leaving Tha Khao Pier. This trip will cost you 150 THB for the longtail boat, 100 THB for the bus to Krabi, 50 THB for the bus to Ao Nang and 100 THB for the longtail boat to Tonsai.
Total: 400 THB
Make sure the bus from Thalen Pier to Krabi drops you off at this bus station: