It's free on IOS and Android, but they have ads for the developers to make money. You have to pay for the PC Version because there are no ads, and you get the all of the skins and hats without having to pay extra.
but here’s the thing you can 100% run a .apk (Android application package) on a chrome I try it before and it works trust me :) and I hope this message makes people understand me better.
Bluestacks can be super intensive on Low-end computers like chromebooks. Unless you have a very expensive pixelbook (which isn't even worth it) you probably won't be able to play anything at a playable frame rate.