"Water is more costly than gasoline."
Not so, actually. Water just pools up on top of the ground, makes oceans even. There's considerable effort and tooling necessary to get to oil, and $B's of technology necessary to refining it into gasoline. The return from refinement in terms of energy that can be carried about is very high, however. This makes the massive construction necessary to anchor wave energy extraction technology horribly less beneficial, because you can't carry it around as electricity, but have to stick it in far less efficient batteries.
And, making batteries is a whole 'nuther massive industrial expense, that all contributes to a watt/kilogram able to be conveniently packed around a fraction of what gasoline provides.
When you translate those costs to places tens of millions of kilometers away from the massive factories necessary to produce portable power, stinky bugs can create orders of magnitude more efficiency.
Thanks!