I don't know any artist who charges less than 25$ for a character portrait. There's some who offer freebies occasionally, but those might take 3 months if they're actually ever completed.
If something is small or only partially done and takes a minimum-wage-compliant number of hours to complete, I might, because I'm not actually very qualified.
But a decent single-subject painting with an abstract background done fairly rapidly apparently takes me 5 hours, so you know, something that quality probably wouldn't be under $25. Sketches are quick enough to get away with a bit though.