I went last year (07) by myself, just barely making the min weight of 130, and then again this year (12/26/08), tandem with my mom because it was so windy and I'm just barely the min weight still so I would have been thrown around up there. I love it. I wouldn't have ask to go back if I hadn't. My mom was really nervous about going, but she ended up loving every minute though..
As for reservation, both times we walked right up and got on the next boat. This year, the guy working said it was their busiest day of the month (12/26). He also said that from Jan 2 through the 10, they had no reservation. Another thing he told us is that alot more people have been walking up and scheduling, or calling while they are down there (the day or two before hand) while in past years, people have been making reservation 6 months out. (My mom and I talk to people alot... =] ) So depending on when you are going, you can walk up and get in, or you have to make a reservation.
I don't know the price though sorry. Have fun! =]