Cost and time aren't as important to me as comfort, which trains are better for than planes (in my admittedly limited experience; I've been on one of each in the last 10 years). There's not much point in going to a LW meetup if I'm too rattled to think straight when I get there.
Three hours might not be too bad, though. It still comes down to how interesting the meetup will be, whether it'd be worth it or not.
We'll be having a Less Wrong meetup on Tuesday, October 12 at 7:00pm at Green Street Grill 280 Green Street Cambridge, MA, to coincide with SIAI President Mike Vassar's visit to Boston. See the meetup.com page. This is in addition to the monthly meetups, which are on October 17th and on the third Sunday of every month.