Depending on how simple/detailed and how large the actual file is (not the one you would put as your sig but the one you would keep for yourself) I'd say between 15 and 30USD.
Hey! Sorry but I'm actually only able to pay in tbt atm I have lots of medical bills to be paid from ER visits and stuff so unfortunately I can't afford to use RLC for art; hope you understand! If you're willing to take tbt for it though i would definitely be interested!