You can get a Batelco SIM from mrsimcard.com with a data package.
Bahamas Sim Card. Batelco Bahamas - Mr. Simcard - +1.5712529901
It is not a great deal. The only other thing I can suggest is iPhonetrip which has included data roaming in the Bahamas and making your calls VOIP over 3g. You have to buy a week's worth of service, but I think it will give you data on many cruise ship lines as well. The problem is that cruise ship GSM data is often at GPRS speeds or worse.