My two cents

Most of the time I don't have to think about how much I need to pay research participants because most of my projects are:

• Either internal, which means that research participants are the employee of the organization and therefore they participant during work hours for which they are already paid.

• Either use recruiting services like Testing Time, Usability Hub or Pollfish that take care of defining and paying the incentives.

But if you have to define yourself what's a good incentive for research participants, the recruiting service "user interviews" has tried to answer this question with their report called "2022 Research Incentives Report" based on data from nearly 20,000 moderated and unmoderated research projects.. You'll find for example in this report this table:

With that data they have also built a UX Research Incentive Calculator where you can answer a few questions and receive per email an estimate for a good incentive.

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