I am willing to pay about 110Zloty (25euro) per month
For this amount you will get more than you expect in most of Polish networks.
I checked first random provider - Play - and for 95zl per month they offer unlimited internet with full speed available.
You have to purchase Play Internet na KartÄ™ sim card - starter for 50zl (for this you have 12gb of data in a year free) and for no limit internet (in one month) you buy extra 'Nielimitowany transfer' for 45zl
play.pl/uslugi/pok-miesiac-bez-limitu/