It's funny how people complain about Slack pricing but I've been using it for our company (nearly 100 people) for nearly a decade without paying a dime. The only thing we're not getting is history (and you really shouldn't save valuable info on chat anyway, we have other data repositories for that such as Wiki and git).
So for me, we're getting tremendous value out of Slack and not once have they bothered to ask us to pay.