It's hard to do pricing because there are so many variables and it's about finding that fine line between your art quality, how long it takes you, and fair wage. Imo I'd price the chibi in your example for 10$ and headshots for 5-7$ (just estimates). Of course as you do more and get better def bump up pricing ^ ^ this is just for u to get an idea
in my personal experience with pricing, I ended up getting way faster with doing quality work and so I could price my work in accordance to the minimum wage in my area