- "Cosplay is just overpriced costumes."
Firstly, costumes in general are pretty pricey. They're pricey because they're specialized, and because people aren't going to wear them that often. In general, the less often you're likely to wear something, the more expensive it is. That's just the way it goes.
Secondly, so what? What do you have against costumes? Costumes are fun; that's why they sell Halloween costumes for adults even though they don't go trick-or-treating. People like to dress up and be something they're not for a little while. Most people don't get this chance but once a year, but conventions give people a chance to do it a little more often.
- They put up a picture of a fat person or a man cosplaying as a female character and make fun of it
It doesn't matter if the cosplay doesn't look good on them, because that was never the point. It's a nice bonus if the costume is realistic, and extremely accurate, or if the actor happens to look a lot like the character, but that's not the point. The point is to have fun. Cosplayers work really fucking hard on their cosplay, spending lots on time and money on them. Many of them are homemade. Quit making fun of it.