Before you get your banner designed, you need to answer this critical question: Where should you get it designed from? There are different kinds of services available that can create all kinds of creative graphic designs for you, including banner. For example, you can hire a graphic design company to create your banner for you. Or, you can visit different freelance design websites and post your project there and let designers bid. Or, you can even go to different online discussion forums where there is a dedicated section for services and you can search for competent and affordable designers.
So, as you see, you have lots of sources from where you can get your banner designed. All these mediums offer unique benefits, but you might even notice some drawbacks as well. So, you need to first analyze all the options and choose the one that can best fit your budget and meet your requirements.