Unless it's changed, you can still go to the ViewTube without actually having to pay for a talk. You get a pretty good view of the Olympic site just from the Greenway, and the cafe is lovely. If the classroom is not being used, you can go upstairs to the viewing platform. I took a group a couple of years ago and got the DLR to Pudding Mill Lane and then to Stratford where we had a bit of a look round, a look at a big model of the proposed developments (Olympic Village and development/regeneration of Stratford) which was in the Library (not sure if it's still there now) and students did some questionnaires, environmental quality assessments, etc.
I don't know how much it cost, but our PE department have just had a day trip to the Olympic Village and a good number have told me that I'd have liked it because it was much more about Geography than PE! I can try and find out a bit more about what they did tomorrow if that would help.