The cable car can be used by cycles which is close enough to the blackwall tunnel to ensure there is never a case for opening the blackwall tunnel to bikes. Although at £9 a go (or £1.70 if you can commit to using 10 trips over the year) I think I would find it a little frivolous to commute using it every day if I needed to go that way.
Cash fare is £4.50 or £3.50 if you use your Oyster/Contactless