What would it cost (if still possible) to do a state and federal return with one W2 and no itemizing for the year 2015?

You cannot use TurboTax Online to do tax returns for 2015. TurboTax Online is only for the current tax year, which is now 2016. To do returns for 2015 you have to use the CD or download TurboTax software for 2015. You can purchase a download at the following link.

http://turbotax.intuit.com/personal-taxes/past-years-products.jsp

For just a W-2 you could use Deluxe, which is the least expensive version available. It costs $69.99, including the state. Sales tax might be added, depending on your state. You might get a better price from a reputable online seller that still has TurboTax for 2015 in stock.

TurboTax does not allow returns for past years to be e-filed. You will have to print your 2015 tax returns and file them by mail.

Or just print the 2015 forms and instructions from the IRS and state tax websites, and do them by hand.