The Personal Edition of Unity (used for training) is free, but the professional version costs from $75 per month. But you'll only need that when you are selling games.
Unity is more complex than the other tools here, but it's not difficult to learn. And there are lots of resources available for Unity developers. Alongside tutorial videos and sample projects, there are developer conferences and a massive (and serious) community.
If you are serious about being a game maker (either as an indie developer or as a professional), then Unity is the tool to invest time learning how to use.
Here are some of the best Unity courses to follow:
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