I am not aware of any academic work on this topic, but that is what is needed. In literary studies we have for a long time paid attention to questions of readership, distribution, advertisement and cognate areas. Influenced by the once entirely separate field of the history of the book, we have paid increasing attention to publishers, booksellers, bookshops, nd other sites and mechanisms of distribution. Literary studies is a heavily resourced field. Music less so, not least because a large part of music studies is practice-oriented (performance and composition), the technical barrier to entry is high, and the scholarship of the kind which would be useful in answering the OPs question is thin on the ground, not least because there is more fundamental work yet to be done on basics as far as the last century or so is concerned. This work - or some of it - will I think eventually come, in the same way we understand to some extent at least how earlier markets for music functioned (e.g. Handel, Mozart) and, while I haven't checked it, I imagine we have a similar level of knowledge re. big names as to the personal finances of e.g. Bartok and Ellington. Now I don't follow music scholarship very much and there may be more out there than I suspect, but I should think there is much further to go in the study of venues, publications, advertising outside specialist publications, and we probably haven't made much of a start on jazz producers, record stores, etc. I daresay there is more of this kind of thing on e.g. rock, punk, pop. All that said, I haven't done much of a search on this, and if people are aware of good sources it would be useful to see the references posted here.