If someone wanted to buy the ship outright, it would be expensive to do so. Dockyards provide more than just the end ship as there are lot of different rewards and sometimes other ships provided as well, such as the Huron in the coming Dockyard.
As others noted above, you are only required to pay for 6 Phases if you want the Puerto Rico. This is the same format as all our recent Dockyards. If that doesn't interest you, please feel free to play out the event and get whatever stuff is available in the first 34 phases (or however far you would like to complete).