That would leave only about $1 billion for public transport, walkway and cycling improvements above the council's "basic" option.
"We think the Auckland Plan is too much of a wishlist and it's not affordable," said Generation Zero Auckland director Dr Sudhvir Singh.
"We have done the costings for a very comprehensive public transport and cycling network for an additional $100 million a year. That would allow Auckland to have a congestion-free network and a turn-up-and-go frequent public transport network serving the entire region."
The Auckland Plan would require either $2 peak-time motorway tolls or a combination of raising petrol tax by 12c a litre and raising residential rates by an extra 15 per cent over 10 years on top of the 57 per cent increase already built into the "basic" option.
Transport Blog editor Patrick Reynolds said the rates increase option was "not really practicable or equitable", and motorway tolls should not be imposed until commuters had a viable public transport alternative.
"New Zealanders have shown a tremendous lack of enthusiasm to pay even a small toll, so it's almost certain that people will take every opportunity to avoid tolls, in other words the local roads are likely to become flooded by structural rat-running," he said.
"The poster cities for road pricing - London, Stockholm and Singapore - all have complete subway networks and busways and cycleways. We are attempting to do that before we have that network."
Auckland Business Forum head Michael Barnett said motorway tolls would be fairer than rates and petrol tax hikes, but he said the council should consider a third option of selling assets such as the port.
He said it would be dangerous to drop roading projects such as Penlink, Mill Rd and Lincoln Rd that were needed to cope with population growth in those areas.
Registrations for tonight's debate have already filled the Aotea Centre's 650-seat NZI conference room.
Transport debate
What: 'Auckland Conversations - fixing Auckland's transport.'
Who: Mayor Len Brown, Pippa Coom (Waitemata Local Board), Patrick Reynolds (Transport Blog), Dr Sudhvir Singh (Generation Zero), David Warburton (Auckland Transport), Peter Winder (Auckland transport funding consensus building group). MC: Fran O'Sullivan (NZ Herald).
Where: Aotea Centre.
When: 5.30pm today. Registrations closed.
On the web
www.shapeauckland.co.nz