Ive easily spent over 100 on commissions. This is because of the quality of the work. Usually this has to do with plushies but For awesome work I'm willing to go that extra mile and I do what I can to help the deviants on this site. I'm always commissioning people on here! ><!
If you are looking to set prices my teachers always say that if you are good and trying to get out into the world, dont charge anything less than 20% below a professional. I don't know any standard prices to tell you so this information is virtually useless but yet I feel that it depends on the size and medium. Traditional media should cost more because you have to buy the media, and if its huge regardless of media it should cost more. Digital drawing takes time, so charge by the hour, mixed with a set size price and then you're set. But I too am a poor art student. 100-150 is a nice range