Using the TurboTax website to e-file the extension request does NOT require you to purchase anything from TurboTax.
You do need a User ID for your TurboTax account which you already have since you needed that account information to enter the license code on the Premier edition you purchased.
I just went through the website for e-filing an extension and never once was asked to purchase anything.
https://turbotax.intuit.com/irs-tax-extensions/
