I can't give you an actual price to charge, but you need to consider cost of materials,
time involved in digitizing,
time for testing your design,
compensation for your skills and talent.
I've head that some people charge a minimum of $5 for set-up,
$1 per thousand stitches, and $1 for each color change.
As you know, the time to embroider the design can be lengthy, and does require you to babysit the machine. Don't short change your skill or time. :wink:
Edit: One last thought. Is the embroidery business going to purchase the design from you, or will you retain all rights to your digitized design...something to consider.