From DWR: “The cost estimate for the short and long tunnel options is $7.3 billion and $7.5 billion, respectively. These estimates do not include environmental permitting or mitigation or Initial Dual Conveyance Assessment power facilities costs. Combining the cost of facilities for the Through-Delta Component with the costs for West Canal Alignment to create a Dual Conveyance System produces a range of total cost of approximately $8.6 to $17.2 billion.”

http://www.water.ca.gov/news/newsreleases/2008/061908assessmentdual.pdf

This price tag is without full engineering designs or specs. As always, we need to expect feature creep and changes to accommodate technological discoveries during the design and spec phase. Most recently, DWR has talked about the long tunnel option and making it deeper to better accommodate the Stockton deep shipping channel. I also seem to recall that the state also needs to buy some of the central delta islands as well but this is not part of the estimates given for the peripheral canal.