I contacted the Bahamian embassy re this issue - here is their reply:
Reference is made to your email dated 29 August, 2013.
If entering The Bahamas by boat, there is a flat fee to clear Customs and Immigration, which is $150.00 for boats 30 feet and under and $300.00 for boats 31 feet and over. This covers a vessel with three persons or less. Also included is a cruising permit, a fishing permit, Customs and Immigration charges and the $20.00 Departure Tax is waived for up to three persons. Each additional person above three will be charged $20.00 Departure Tax. If you plan to stay longer than 12 months, special arrangements must be made with Bahamas Customs and Immigration.
This information can be found at: Entry Requirements | The Official Site of The Bahamas
Thank you for your interest in The Bahamas.
Embassy of The Bahamas
2220 Massachusetts Avenue, NW
Washington, DC 20008
Telephone: (202) 319 2660
Facsimile: (202) 319 2668