As there have been a number of posts about book covers lately I thought I would throw in my 2 pence, for what it is worth.
You can get a cover designed for you at Fiverr for ...wait for it, just five dollars.
Or, if you are on a real budget you can purchase the right to use photographs, illustrations, etc from a stock photography website for as low as two dollars.
You would need to sell an awfully large number of books to recoup some of the costs I've seen mentioned.
If you have a wonderful product on your hands and you can afford to pay these prices then by all means, go for it.
But, if like many on here, your have no way of knowing if your book will sell try out the budget version before you sink yourself into debt.