I play for free. At the point I'm at in the game, i don't need any other weapons. For the advance ships, I just join random crews of subscribed members and sink ships on their ships-works well since the captain still gets his money.
I am considering upgrading later on whne it's more vital. I was so ticked when I sailed to Cuba, took me 3 tries, and when I got their found out to get VooDoo I needed to upgrade
