TIP : If you want to pay a lower sum for graphics work just make a deal with someone who has a good portfolio, don't do a contest, because no one wants to complete with 15 other people for the POSSIBILITY of being poorly paid. Contests work because there is a big tempting wad of coins waiting to motivate them. Just my opinion as a graphic artist.
This +1. No one's going to waste their time just for a chance to be paid a paltry sum. Try hiring a graphic artist directly, and communicate changes to him/her directly.