The toughest mile of the aging Alaskan Way Viaduct could cost as much as $3.5 billion to replace if the state chooses one of two tunnel options. But the cost could be as low as $800 million if the viaduct is replaced with surface streets.

The toughest mile of the aging Alaskan Way Viaduct could cost as much as $3.5 billion to replace if the state chooses one of two tunnel options.

But the cost could be as low as $800 million if the viaduct is replaced with surface streets.

The state on Thursday released its cost estimates, and digging a deep bore tunnel would be the most expensive of eight options, at $3.5 billion. The cost of a “cut and cover” tunnel came in at $2.7 billion.

The least-expensive replacements would be surface options ranging in cost from $800 million to $900 million.

The state will narrow the options to two or three in December. Gov. Christine Gregoire will then choose a preferred option by the end of the year.

The Legislature appropriated $2.8 billion for replacing the viaduct, but the state has already spent or committed more than $1 billion, mostly on rebuilding the south end. An elevated viaduct or a surface option could be done with available funds.

Rising materials costs would have boosted the prices even higher, but in the last few months, the state has been looking at four-lane highway designs, instead of the six-lane versions favored earlier this decade. Transportation Secretary Paula Hammond said the change has helped keep an elevated version, for example, close to the $2.8 billion previously allocated.

The cost of the most-expensive choice — the $3.5 billion bored tunnel for the central mile — is far above the money earmarked by the Legislature.

But Ron Paananen, who heads the state Department of Transportation viaduct project, said that doesn’t mean a tunnel option is off the table.

“It’s too early to answer the question, if there’s enough money,” he said.

Paananen also released a document listing 56 other funding possibilities, including federal congestion mitigation funds, tolls on state roads systemwide and even the sale of naming rights to a new viaduct.

Other options could add to the costs: adding another lane to northbound Interstate 5; adding more streetcars downtown and in Seattle neighborhoods; greatly expanding transit; and requiring that businesses subsidize transit passes.