If you can't afford to hire a graphic artist to make your custom book covers, then consider premade templates that can be customized to fit your story. Many of these professional templates come in mega paks with multiple designs, fonts, and artwork that can be edited into a whole new cover design. The two Kindle book cover designs on this page are from the same template just to give you an idea.
Next, you can customize the templates at will if you have Photoshop. But what if you don't have Photoshop? Not to worry!
If you're not a graphic designer, or don't have Photoshop, simply purchase the template mega pak yourself, pick out the design you like, and send the Photoshop files to your graphic designer. They can customize the template to your liking. And since much of the work is already done, you should save big on all your custom book covers this way.