A few Werks ago, I sold my Xbox one and with that my only working controller for my PC. Since then, i have been playing hollowknight and Jedi fallen order on my old Xbox 360 controller with its unlikeable d-pad, even after multiple mods to it.
And with the steam controller coming, im eagerly awaiting the steam controller
My guess is about 100-150€, since the price of a General controller with back buttons and no Hall effect Joysticks or touchpads is already about 100€, so this + all the cool shit steam is doing will be more.
That seems expensive, you can get hall effect or even TMR sticks and back buttons for well below that. That said, I do think the Steam Controller will be more expensive than that. 80-100€ is my guess.