Another way to look at it is like the long arm quilters do
Although the rates vary, for something like this, they charge by the square inch ( $0.015 - $0.03 per square inch) , then plus a per linear inch charge to put the binding on (one of the sites I checked charged $0.22/linear inch of binding to prepare, stitch binding on and then hand stitch the binding to the back) , and then an overall fee if the quilt is not ready for the long arm machine (squaring up backing and batting around $15 - $20 per quilt)
I would lay out a simple table
Quilt 1 Dimensions X x Y
Total Area Z square Inches
Quilting Fee ( $0.qqq/sq In X Z sq.in.) $ xx.xx
Binding Fee ( 2 X (X + Y) * $0.22) $ mm.mm
Repair & Sandwiching Fee $ kk.kk
Total Quilt 1 ___________
$ss.ss
This way even for yourself, you will get a clear picture of what you will charge for each quilt and you can clearly communicate it to your coworker. Also I would put in WRITING, that they will provide the batting and backing, thread and binding, or agree provide you with funds up front to purchase these items. If they are not quilters it might be easier for you to do it.
I would prepare a quote again, provide them with an invoice for materials, then purchase the materials.
I know this sounds "business-y" but you don't want any confusion about what your are doing and charging for.
Hope this helps Mary in MA