I kinda hold the same mentality...
I don't charge by the hour. I charge a base labor fee depending on how complex the outfit is, then I add on fabric and shipping.
I just don't think that people would want to pay $400 for a cosplay. I know I wouldn't.
I am a college student and right now commissioning is my only source of revenue, but really I don't need to make that much anyway, so it's ok if I don't.
I also want to say the most I've ever charged for a costume is $200. Again I don't live off of this, but I do use what I get for all my con going, costuming, theater going, etc. I don't think getting a good costume should charge people an arm and a leg.