[UPDATE 2: Apparently the McGinn plan is not exactly the WSDOT surface/transit plan.]
[UPDATE: As commenter Chris points out (and confirmed in the report), the $200m in savings on Moving Forward is actually due to putting less money into the Battery St. tunnel and the viaduct North of Lenora St. Most or all of this money would have to be put back in for the Surface/Transit option. This reduces the Surface/Transit option savings to roughly $100m-300m plus overruns. We're still peeling the onion.]
I just chatted with Kadeena Lenz of WSDOT, who pointed me to this report (pdf). The Moving Forward project cost has dropped from $1.1 billion to $900m due to some unanticipated savings from not having to redo the Battery Street tunnel; of that, $300m is supposed to come from the Port of Seattle, and $600m from the State.
McGinn doesn’t include port contributions in the budget, so I think it’s fair to score this as a $600m $800m shortfall in his budget plans, not $1.1 billion. (Split the difference!). To get his surface/transit plan, delete the $1.9 billion tunnel from the chart above, add $553m for I-5 improvements, about $170m for transit, and about $200m more for local roads. Then remove $400m in tolling, and you get a little under $600m $800m not covered by the State, the feds, or the Port of Seattle.
Oddly, aside from the moving forward issue, McGinn’s cost estimates for surface/transit are about $175m higher than Nickels, so you can give him credit for that difference if you like. It also has to be said that the cost overrun risk is lower for surface/transit than the tunnel.
The bottom line: assuming the State and Port are willing to spend $2.7 billion no matter what, surface/transit is cheaper for the City and County by $300m-$500m $100m-$300m, but it isn’t free.