You can do whichever you like. If you're needed as a static marshall you are not obliged to register; if you can be arsed to raise sponsorship you can do the £12; and if you just want to ride it go for the £35. The danger of lots of people not registering and offering to marshal is that there'll be too many marshals but a drop in the money raised. Tis a charidee jaunt, after all . DZ said he'd sort out the marshalling next week...
OK, you've shamed me! £35 it is!
Although it may leave me short of funds in The Seagull!