I can't afford to pay pro artists, but I am slowly replacing my original framed astronomical photo covers with better self-made designs. I was foolish not to do this in the first place, but live and learn. My new covers at least look like real paperback book covers, illustrating book content. What I do is use Adobe Illustrator Elements to combine material from public domain photos, make the color schemas match up with the software. Then I draw foreground art using traditional art materials (pencil, pen, watercolor, etc,), use the software to make it look more photographic, then insert it into the background. It's not great, but it's way better than what I had before. Right now, I'm working on a cover that shows the Crab Nebula hanging huge in the sky over the Red Desert of Turkmenistan. The hard part is placing an ornithopter against the sky (I am using a highly-modified peregrine falcon), then my main character in the foreground pointing a gun at the audience. That starts out as a photograph of me when I was 27 (38 years ago!).
Unless you are a professional graphic artist, you are not qualified to design your own cover. This is the one case where you should NOT skimp. I used ebooklaunch.com. I highly recommend them, both from the standpoint of service and from the quality of their work.
Only way to tell for sure what your ebook will look like to the final buyer is to buy it yourself. (Just realize that once you buy it, that's the version you will always get if you try to buy it again. Only way to get a new version, if there is a new version, is to ask the Zon to push the new version to your Kindle.)
I too have been impressed with SelfPubBookCovers.com.
If you have an idea in your mind of how you'd like your cover to look, I suggest you check them out. .
In the past I used Fiver with mixed results.
The hard part was trying to convey to a third party the picture I had in mind but when it came to the cover of WHERE TO FIND THINGS WHEN I'M GONE,I found a student in Pakistan who did a fantastic job.
More recently I tried SelfPubBookCovers.com to create my own cover for GUILTY UNTIL PROVED INNOCENT.
Easy to navigate, and if my memory serves me correct it was about $69. Joseph (a regular contributor to this forum) made some suggestions on how I could improve the image and I took his advice as I was able to go back and make changes at no extra cost. Here's the result.
I do my own covers, using my own stock of photographs and MS Publisher.
They say a picture can say a thousand words. If you pick out one background photo that just says it all and has a lot of impact, and then perhaps overlay it with a semi-transparent image of something related, and do your text colors and placement right, you can get a lot of mileage.
I go to the Deviant Art jobs forum. There are a LOT of good artists on there looking for work. You post on the forum, just like here, say what you want and what you're willing to pay and people send you messages with offers. You look through their portfolios to see what kind of skill and type of work they do and pick one you like or none at all. It's just a forum, so no commitments. I pay all mine through paypal with part up front and part after finish.
I'm going to suggest fiverr.com as it's cheap and if you don't like the first one, try another designer. Tip: research the covers and fonts you like. That gives the designer a heads up as to what you want.
I design my own covers. I've used both Gimp and Canva. I like them both. Gimp is a little more detailed but Canva has a lot of excellent graphics for not much money. You can also buy a graphic elsewhere and upload it to Canva. When I want to use some techniques unavailable in Canva, I use Pixler to make those alterations.