North Greenwich tube car park is £11 all day although will probably be full, but if you can get there extra early or even in morning then you can get a space.
No idea how long WWE events go on for, but if less than 4 hours you can park in cinema car park which is opposite the Emirates Airline ski lift type thing entrance, order a cinema ticket online from Cineworld website and you get free car parking for 4 hours. We have regularly done this and have had no issues parking there, we live about 20 mins drive away from O2 and have Cineworld passes and pay £16 a month for unlimited cinema trips, so it effectively costs us nothing when we use their carpark but don’t actually watch a film, and just go for some food or a gig/event there.