The day starts around 9:45am. You'll get a welcome from the dean and then hear some presentations about curriculum, research, fin aid, etc. You'll then have lunch and some ms1/2 will eat with you and you can ask them questions. Then the group is broken up and you'll either get a tour with some ms4's or have your interviews.
Interviews are ~30 minutes with a 10-15 minute break in between. You then switch activities.
As for expense, flights are flights. But for lodging, a bunch of out-of-towners stayed at the Boston Hostel literally across from the med school. If you do a shared dorm room, it's like $45, or a private room for $100. I did priceline "name your price" and stayed at the Park Plaza (10 minute walk) for $90.