I do not recommend Fiverr for artwork. I have seen multiple artists over on their site with THE EXACT SAME portfolio (so someone is not telling the truth). When I asked one of the artists about it, I was told to "Mind my own business." 


With this in mind you can always use www.canva.com (which starts at free). I've used Kappa99 for a ONE OFF service (around $50) and I've used Podcast Designs (around $85). Podcast Designs 


Designcrowd is a crowd sourced competition site where you can see many designs and pick your favorite (prices start at $99)