Went this past Feb. I can't remember exactly, but It was either $8.00 or $12.00 per person round trip. Hope your taxi ride is better than ours was. We hit a cement truck. But the water is beautiful at Coki beach.
From Havesight it should be about $6 per person each way. From the old sub base it should be about $ 8 perperson each way. With gas prices the way they are, don't be surprised if at the end of the ride the driver makes up a "surcharge".
Ask the price when you board, if the taxis are being assigned by a "superviser" ask him how much the ride should be and confirm the price with the driver.