The taxi fare is around HKD100.

it might be more than that, i presume, since you would be changing islands (from kowloon to hong kong island) and ocean park is quite far. cheaper alternative is for you to ride the mtr and alight at admiralty station. go out (i believe it is exit b, i'm not sure though) then ride the bus going to ocean park.

however, if you are a group of 4 maybe better ride a taxi because the taxi fare would be same or slightly higher than using mtr and bus. the difference would be the comfort and convenience.