An Expo Pass is only $25 if you register before December 1st, $45 after that.
Conference passes very by conference type so check the registration site once it opens on Sept 2nd to see all the different packages and pricing.
It's as inexpensive as free and as expensive as you'd like to make it.
You can get free Exhibit Hall Passes all around the Mac Web in the weeks to come, depending on how far away you stay you can get cheap hotels and you can take city buses to get around town. There are also lots of cheap places to eat.
The above may not be very comfortable though. :)
The closer you stay to the Moscone Center, the more expensive hotels get. Stay as close as you can afford though - Expo can be exhausting and that "short" 5 block walk on Monday back to the hotel becomes a Bataan Death March come Wednesday. :) If you have to, double up on a room with a buddy to make it cheaper.
Registration will go live on September 2nd. The website you will register from is www.macworldexpo.com.
Macworld is a great event for EVERYONE! There is both a Conference & an Expo so when you are registering be sure to check out all of the packages to find the best one for you.
I recommend you book your flight as soon as you can. I booked mine from NYC to SFO about a month or so ago, and I'm glad I did. The fares are going up as we speak. I also booked my hotel when the hotel list came out. I'm not sure how fast the desirable hotels get booked up, but I wanted to stay close to the convention center, so I reserved my room right away.
I've gone ahead and booked early myself. I'm UK based as well (Stockport), so have booked flights out from Manchester on the Sunday through Sky Travel of all places - they had the best combination of Flight and Hotel after LOTS of searching. Definitely a Billy-bargain price though.