People pay lots of money for brand name clothing because it is a brand. You have to establish that brand first and make it something that people think will get them laid. Then, they will pay you ridiculous money for simple crap.
On the other side of things, if you are going in the artistic niche, small run, well designed shirts can often fetch $25 a pop.
Not to be a dick, but half your designs are just a custom shape object dragged around a few times. I am sure that there are people that will like it, but there are several people that will see it as lazy design.