it depends how long they take you! :) i like to price my art depending on time length and how much it hurts my hand, ahaha.
if one of those pictures takes you say... an hour? price it accordingly - for every hour, increase the base price or whether the pic is bust/waist/fullbody. find a base price however. If its just lineart, your lines seem fairly clean, so maybe 7$ - 8$ or so? and if there's flat colour added, maybe 10$ or 12$ and if theres' shading added, maybe 13$ - 15$? I'm honestly terrible with pricing as well, but the trick is to start at a base price, and if you get no bites for a while, adjust accordingly (that you're comfortable with depending on how long a picture takes you, make the price higher if it takes you more than an hour or something along those lines)
i hope this helps somewhat!