The official car park is £30, there are some other options, can be slow to get out, 40 minutes last time. But the others they either involve a longish walk or other transport. We have taken the cable car and parked north side not much cheaper for parking and you have the cable car ticket but added some extra fun for the kids and was better getting out and no black wall tunnel. A friend parks at canary Warf or Stratford and trains it in but can get busy. There is a short stay there that’s cheaper but not sure on the rules for using it.