I own a jazz record label and have produced more than 55 jazz records. I do most of the photography for my own label, but also have done photography for jazz artists for pay.
You would need to assess the overall economic situation to set a price.
Are these wealthy people out to boost their musical hobby? Are they under-recognized artists struggling to make the rent?
Do they care whether their cover photograph is good or not? Not all know the difference, or even care. Do they see the value in your photograph to boost their public profiles? They should see that, if you're good.
Sad to say, that very few jazz records break even outside of pop-jazz records for major labels. As an economic proposition, there is not enough money in the system to pay everyone.
Where you really can make a small payday is where the artist is self-producing a release in preparation to make a major move. You can sell them on the idea that their photograph will sell /the artist/ as well as their record. Every artist with any ambition should have a hero photograph that they can send to press. A good one really does make a difference, and you should educate the artists on the value of having a "real photographer" do it. Rarely can you charge full rate, but if the artist has money in his/her background, then you will need to stand firm in the knowledge that the artist can really afford to pay for what they get. Many artists have families who are willing to put up -- on a one-time basis -- enough money to do a debut recording properly. After that, it's another story.
But remember, you have very little leverage, and should be prepared to walk away if you think the arrangement does not benefit you sufficiently, either monetarily or in spirit. I have had several famous photographers do work for my label while refusing pay. There isn't a real market with supply-and-demand pressures there.
But in the case where you have an artist with money in his/her background, I would not do the work for free, and would charge somewhere around $200 for one photo session and about 5 images delivered.