50 would be the base for the digital, but i think 100 would be too much for the headshot ;v; you should get a better angle on the traditional art (like laying it flat on a surface then take a picture of it)
You do a great job with shading/highlights, I just suggest working on proportions and possibly focusing the camera before taking a picture. Try working with hands too if you can -- I know it's pretty frustrating, but it's worth it after all the practice. As for digital art, the eyes are a bit too low and the shoulders should be more broad. A fair price would roughly be around 75-80 tbt