This is the same about what has been said about writing a description and producing a video; nobody expects you to be the best designer in the world but there are so many possibilities to create artwork that at least looks decent – even for people who are the least creative people on the planet.
We suggest having a look at Canva.com. I can’t think of an online design-tool that’s easier to use than Canva. Canva comes with a huge list of premade designs that can easily be adapted to your needs. Various formats help beginners to create a decent looking design in a few minutes that can be used on various occasions, from social networking up to print. And the prices are more then affordable, $1 for a complete premium design, including stock-photo really is a bargain, some designs are completely free!
Depending on the size of your event, it might be interesting to have real logo designed. 99designs.com is a marketplace that connects you to designers around the world for affordable prices. They also have ready-made logos for $99 which you can be adapted to your needs.
Again you should also look around if you can find someone around you who can help you out with some artwork or design-skills.
No matter how you choose to do it, you should know where you want to use the artwork and how. Making a small image and blowing it up then later to a full format image on Facebook or even worse for print doesn’t work. You’d be better off making various versions of one design in a range or sizes so that you have it ready for all occasions.