So far I've encountered four rail carriers (besides PKP Intercity) which offer rail service in Poland, with lower prices and far more departures than PKP.
>Łódzka Kolej Aglomeracyjna
>Koleje Mazowieckie
>Arriva
>PolRegio
Their services often do not show up on Google Maps, particularly for the second two. You have to download each company's app and search for tickets on it. Undoubtedly other regions of Poland also have their regional transport companies.