It depends on your level of graphic design experience/skill, and how much you’re willing to spend. Overwhelming consensus is not do it yourself if you can avoid it. Creating a truly effective cover that attracts readers is a science. A cover that an author thinks is cool may not be the most effective at driving sales, pre-order or otherwise. You will get a pro cover design from Inkshares if you get funded. But it can only help your campaign to have an effective cover upfront.
If you need or want to do it yourself, I recommend checking out these articles.
This is a huge list of resources for authors designing their own covers. This guy also runs a monthly book design contest. You can see his feedback on each submitted cover. It’s a great way to learn what works and what doesn’t.
A good 9-step series that walks you through the process of making your own cover. The first article also discusses the pros and cons of doing it yourself vs. hiring someone.
Informative article from an author discussing how changing her cover affected her sales.
If you want to hire someone, here are some highly recommended places. These are designers that focus strictly on book covers.
Ebooklauch has several budget friendly packages:
Bespoke supposedly has somewhat flexible pricing too:
Damonza is a little pricey, but their stuff is beautiful. I went with them since I’m promoting my book in several places outside of Inkshares before my campaign. Couldn’t be happier.
Hope that helps!