Kingmakers price
No price has been announced. The Steam page has no buy button and the Epic page shows no price, and there is no pre-order: the studio has said it will not take money until there is a game people can play. Nothing the studio has published points to it being free to play.
No buy button on Steam, no price on Epic, nothing to pre-order. What would change this: an announced price or a live purchase button.

Why you cannot pre-order it
This is a choice, and the game director has explained it:
“We aren’t trying to take a bunch of money from people unless it is for a game they can immediately play, because we aren’t going to put ourselves in a position where we have to cut corners to rush something out because we took a bunch of pre-order money.”
One consequence is simple: if something is selling a Kingmakers pre-order, it is not the studio. More on spotting that on what happened to Kingmakers.
Will Kingmakers be free?
Paid, by every sign
The delay letter talks about the game in terms of charging for it, which only makes sense for a paid release.
“We just need a bit more time on content polish before we feel good about charging money for it.”
Redemption Road. From Steam announcement: A Message From the Developers
By invitation
Requested from the store page rather than bought. How to ask for a place is on the Kingmakers playtest page, and the other things you can do before release are on how to play Kingmakers now.
Editions, DLC and supporter packs
Where it will be sold
On PC. The Steam page is where the publisher points for Early Access, and the official site also links an Epic Games Store page that currently reads Coming Soon. Whether both stores open on the same day has not been said. Store details and operating systems are on Kingmakers on Steam and Epic.
Where a price will show first
On the store pages or in an official announcement; nothing has said which comes first. If a date is announced it will show on the Kingmakers release date page.