I've briefly touched upon this topic before but here goes; I know you can play D&D for pretty much free because it's extremely easy to pirate, but I think we've settled by now that piracy doesn't actually hurt companies as much as they want us to think, meaning that pirating D&D isn't as big of a "stick it to WotC" move as it's often presented as. Of course if you absolutely have to play D&D (but, like, why?) you won't get any moralizing from me about piracy, like, ever.
But the point is: supporting another game either monetarily or with your valuable time is a much more direct and tangible way to stick it to the cultural monopoly of D&D than playing D&D and not paying WotC. I mean if it's another big-ish publisher I don't have a lot of faith in their working conditions being much better than WotC's, but in some cases it probably is so. As it often happens, the market leader can often afford to pay its employees worse simply due to those positions being more desirable.
But anyway who cares, there's lots of games out there where you can actually get a full game sometimes for less than the cost of a single D&D book and since those games are often built as more focused experiences than the D&D "forever game" formula you're actually more likely to get to experience all of the game instead of a lot of the content existing just as shadows on the cave wall.