The following factors go hand in hand in determining the price
1) stitch counts - smaller stitch counts will mean that you spend more time in hooping then in embroidering
2)number of color changes in a design - you waste valuable machine time in trimming and needle changes as the machine stops / slows down/ restarts
3) Design matters - Now this is tricky, A delicate design with blends and intricate details will take longer to embroiderer than a normal oval filled logo with a standard text font,
4) fabric matters - i would definitely charge more for embroidering on a stretchy fabric then a cotton twill or a regular polo shirt
5)Value to customer. Applique has more value to your customer, they expect to pay more.
6) Quantity is the most important factor here - embroidering 15 garments or 50 or 500 will definitely have a impact on the rates.
7)Time frame. If the customer can wait then you will probably charge him less than someone that wants it today.
Large satin stitches not only consume a lot of thread but also makes some machines run slower and if you are running a design with a long satin stitch of ..say.. 9mm and the max stitch length set on your machine then it will take 2 stitches for every long stitch in your design.