I've been online searching for book cover artists. There not only are quite a few online, their prices vary widely.
If you're looking for one, you're probably judging them based on their fees and their sample covers they have posted on their websites. You might also be getting recommendations from friends.
You'll also want to look at what you get for your money. Just the cover? What about rights to use that cover for other things like the e-book version, or book marks, or your business card?
Check out the covers. Do they do the kind you envisioned for your book? Do their covers look professional? Do they fit the genre you're writing?
How much are you willing to pay? $250? $2500? Yes, some artists are paid over $2000 for a full cover, but they usually include other things like certain other rights, making sure the cover fits the requirements of the publisher, etc.
Most of them don't put their prices online because it may vary depending on the job. So don't hesitate to email them. Tell them what you're looking for. Tell them a little bit about your book. Maybe even your vision of the book's cover.
Most will answer back. Perhaps give you a quote and explain what would be included in the package. A few may not answer at all. Cross them off your list and move on.