It honestly just depends on the artist and their popularity, the more popular they are, the probably more expensive it’ll get because they’ll still get sales from at least one person most of the time. Less popular artists charge between $10+, usually the semi realism stuff starts at $25 for less popular artists. You should also take the amount of time the artist spends on an art piece, they would probably feel the need to increase their price if they spent like an entire day on the piece for like $15 (which is understandable). I do semi realism myself and my price starts at $25.