At cons I mainly do head and torso sketches, and occasional full commissions if I have the time. Price goes up when adding more than one figure so if you really want a commission of Lincoln punching Cookie Monster then it’ll cost you.
Also I only do known character sketches. I’ve done peoples own characters before and a few times they have used those as covers on their creator owned book. The problem is, it’s a head sketch drawn at a con, and now it’s a cover? I do put time and love into sketches but not the amount my covers need. It doesn’t represent my name very well to have a con sketch as a cover.