A new tropical coconut tree - straight trunk - found under Decor / Misc. Decor, costs 0. You need Ambitions and to place the package in both the mods/packages (Sims3 ) directory and in the "The Sims 3 Create a World Tool/ Packages" directory for the item to show in your game. There is an earlier post explaining how to install items in CAW.
Importing packages into CAW
Alternatively you can place a small lot near the edge of the sea and place the coconut tree on it. This way you won't be able to adjust the height, tilt or rotation.
Tropical coconut tree - straight trunk (MediaFire)
Galeocerdo cuvier - Tiger shark
Cocos nucifera - tropical coconut tree for CAW