If you hire the services of a charter boat or a flying service to help facilitate scattering of the ashes, the company will charge you a fee for their services. The cost may vary from one provider to another, so you may want to check with several companies to compare prices.
On the other hand, if you are fortunate enough to know someone who has a private boat or airplane, you can take the boat or plane and scatter the ashes yourself.
The EPA (Environmental Protection Agency) requires that any scattering be done at least 3 nautical miles out from shore. They also require that you submit a report of any at-sea burials within 30 days of the event taking place.