If you're already in Massachusetts and want to head over to Nantucket, the easiest way to get there is probably by ferry.
There are two companies which have ferries to Nantucket:
The Steamship Authority
www.SteamshipAuthority.com
Hy-line Cruises
www.HyLineCruises.com
They both leave from Hyannis, MA, and both companies have traditional ferries as well as high-speed ferries.
Traditional Ferry:
The passage takes about two hours, but the round-trip fares are only approximately $30.00 for adults and $15.00 for children 5-12 years. Please note that fares change according to the seasons, so be certain to check out their websites for the current rates.
Both companies allow you bring bikes on board for approximately $10.00 round-trip.
Hy-line Cruises offers an upgrade option to First Class-this allows you access to a newly renovated climate-controlled lounge with private sundeck. I believe the food service is also better.
The Steampship Authority has ferry your automobile to Nantucket. The rates for autos only range from $115.00-$200.00 depending on the size of the vehicle and the time of the year. Please note that you still must pay for your passage aboard the ferry.
High-Speed Ferry:
This method is much faster-only about one hour. However, though your time is cut in half, your price is doubled. The round-trip fares are approximately $60.00 for adults and $45.00 for children 5-12 years. Again, as the fares change according to the seasons, please check out their websites for the current rates.
The high-speed ferry for Hy-line Cruises is called "The Grey Lady". The high-speed ferry for the Steamship Authority is called the "Flying Cloud". Both allow bicycles for approximately $10.00, but neither can transport vehicles.
During peak seasons, reservations are strongly recommended. You must check-in at least a half hour in advance of scheduled departure or risk losing your spot.
My friends and I took the Flying Cloud to Nantucket. The interior was spacious and air-conditioned (almost to the point of being too cold!). The seats were mostly booth-like cushions around a table. There were two levels, and you could go out onto the deck on the second level. There was also a refreshment bar. It was fast and enjoyable, though a bit pricey.