Bahamas population is about 400,000 people. About 3.2 million live in Puerto Rico. I would assume that it would cost more to rehabilitate a bigger place with more houses, roads, infrastructure, all other things being equal.
And only a portion of the Bahamas was impacted. About 70,000 people in the Grand Bahama and Abacos. The death toll is at about 30 now, but expected to increase dramatically as recovery crews can get into the outlying areas that were flooded and destroyed by wind.
Lots of local efforts being made down here to assist our neighbors in the Bahamas. I was at Costco yesterday and people were buying massive amounts of bottled water, generators, food, etc. I have to assume that they are planning to donate them. I have friends who have organized supply donations, air transport, etc. to get medical supplies and other goods over there. I know some who are planning to go over by boat this weekend to deliver supplies. The local cruise ship left last night with volunteers, including about 50 doctors, to go to Freeport to assist.
Still, one of the best ways to help is to donate to the Red Cross or other relief organizations who have the experience and logistics to properly assist the Bahamians.