As a longarm quilter, I charge 3 cents an inch to attach the binding to the quilt by machine. It takes about an hour to do this on a bed sized quilt.
Figure out how long it takes and don't cut yourself short. Figure out an hourly wage. My customers know I will make the binding and attach it for them, but the handwork will take forever. You can also offer to attach the binding to the back and turn it to the front and stitch by machine. It is hard to do to keep it in the ditch on the back, so I use a decorative stitch to do so. It takes a lot less time and will make the binding more durable for baby quilts.
Pam T