From Boston:

From New York:

Taking the ferry from Boston is the best way to get to Provincetown. It's easy, you don't have to drive, and you can have a cocktail on the boat. When you arrive get a cab to 590 Commercial. Done.

From the airport you can take the water shuttle for $10 to the ferry. Take this back again to the airport on your return. Even though you have to catch a shuttle after the boat drops you off, it's still faster (and cheaper) than cabbing it.

Check out the Maps of the Cape and Provincetown