It really all depends on the complexity of the costume. Something that is complex and say involves big dresses, or armor is going to be much more expensive( Maybe upwards of $300), while something rather simple is going to be less (Lets say around $150). I'm possible severely underestimating. Also I think it depends on the level of experience when it comes to the commission. If the person is say a professional costume designer with 15 years experience, yes, they're going to charge more.
Mangochutney said it best, the sellers on Ebay are not making a decent compensation off these cosplays. So comparing prices to that off Ebay is not a great idea, unless the commission doesn't want to make any money. Cosplay is an expensive hobby, and nothing is going to be cheap.
Eren Jaeger (Attack on Titan)
Mitsuru Kirijo (Persona 3)
Saruhiko Fushimi (K Project)
Shadow Yukiko (Persona 4)
Suit! Sarutobi Sasuke (Sengoku Basara)
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