Hate to tell you this, but most of the people who make fun shirts and sell on the internet don't make much money out of it unless it's tied into something else they're profiting from (such as a webcomic or blog). Currently, what you're workign on is going to cost more than you earn, unless you find soem way of chopping down expenses further and maybe direct-sell them at conventions/events.
The only way you can sell $25.00 or higher per shirt online is if you had to personalize each one of them--eg made to order and fully customizable to the order. I know some places sell them for a lot higher, but they also have a lot more pull in that respect (EG DC/Marvel-branded shirts).