I'd also suggest doing it yourself; you'd be kicking yourself later if one of your designs really made it big
As far as getting a perspective or price range on the other option, though, there are websites out there that deal in connecting designers and people (either general, or there is at least one that is t-shirt specific). There has also been some previous discussion on this aspect (though usually from the 'buying' side) in earlier posts; try to search a bit. If I recollect correctly, I think the "norm" for a requested design (someone makes a design to your specifications) was around $150-300.