cost of buying a boat
I am not certain, but I do not think that you can "document" a vessel built outside the country. The only thing I can suggest that you do is go to the USCG site and search for "documentation" FAQ''s....and if the definitive answer is not there...you will have to call them. If you are needing the documentation for a loan/mortgage requirement from/for a bank.....don''t sign the papers until you have your answers.
Other than that....you will be subject to import duties on the boat....and if the present owner says they are already paid, require he/she/them to produce the documents proving it....in originals. Otherwise you could get a nasty shock. If you buy the boat and can''t prove it when you register it.