There’s nothing worse to say to a musician, photographer, writer, or any other artist. “May we use your work? We can’t pay you, but…”
You CAN pay for their work. You really can. Did you buy a coffee this week? That’s five bucks. Two of them? Ten bucks.
How about, next time you ask if you can use someone’s work, you offer them that ten bucks? Or to buy them lunch?
You want to “pick someone’s brain”, perhaps? find a way to pay for it. You can do it.