How can I file just my state? How much does it cost?

[xmasbaby0]

You cannot file a "stand alone" state return using the TurboTax program.  The information flows from the federal return the state return, so unless you prepare a federal return, you cannot prepare a state return. If you use the Free Edition which you are posting from to prepare a federal and state return, the use of the state software costs $29.99.  Your state probably has a web site where you can prepare a return.