Cost?

Just Wondering if there are any surprise costs to the plugin, or upsells.
I went through the initial setup, and haven’t found any kind of pro version, etc.

Concerned, because I don’t want to commit to a new program, and then get skewered, later.
Was using SEOPressor, previously, but they don’t update their stuff, and I finally encountered a fatal UI glitch which has disabled my ability to use the program. ($10/mo wasted for many months)

Interested in RankMath, but want to make sure it’s gonna be a safe investment of my time.
Why is this free, and if there are plans to charge, what costs can be expected?

Thanks…