Here's my thought on the price.
1. If you enjoyed making this quilt and would like to do more of them for others, keep the price reasonable. But keep the price high enough, that it's worth your while.
2. If you hated working with the denim or just would never want to do another quilt like it again, make the price higher and worth your time and effort.
We all have our own ideas on how much our time and effort are worth. For instance in my day job, I make $40+ per hour. Of course, I couldn't dream of charging that much for a quilt. I'm a professional at work. I'm only a novice quilter.