As a side note, on the RA events sometimes artists are listed in the description but not linked in the description so there could be some artists missing. In my experience it tends to vary on the nightclub.
In the EDM world, it can often be much more than a slight premium. Ever since streaming took over music sales, performance fees have become the key source of income for most artists.
I do know some indie artists who make a bit of extra money at performances selling CDs to people who still buy them. I think it takes advantage of the immediacy of the moment, and the fact that a lot of people are actually not savvy about finding stuff online.