I'm thinking close to what Bella suggested - around 3 times cost of supplies. If the fabric/batting/backing costs $75 then his charge would be $225. This would leave a profit of $150. Is that enough profit to cover your time?
Consider what a typical LA would charge you. In my area, I can get a crib quilt done for about $65. If that's the going rate for the quilting portion of the project, than perhaps a $150 profit is in line. It's up to you and how valuable your time is.