[songshuu]

You could use fiverr and a generational model.

generation 1 : write a brief 5 designers @ $5 select your favorite design (be sure to get some outside human perspectives)

generation 2 : modify brief based on what you learned in generation 1. what you liked and didn't like. include the winning design from generation 1 as an inspiration and say you'd like to improve it 5 designers @ $5

for $50 you get 10 designs and have iterated twice

you can repeat this process until you're satisfied.