Do you really have to have a good book cover for your novel? Or could you still sell it even if it just had a plain cover without any illustrations to attract your readers?
It’s generally recommended that you spend quite a lot of money on book cover design, that you don’t hire a cheap book cover designer.
The reasoning for this is, a good book cover design is essential to help you sell your book, a good quality book cover design reflects good quality writing.
However in my view it’s debatable whether this is true. I have seen quite a few good quality book covers that don’t reflect good writing inside the book.
Also, quite a few years’ ago a publisher called ‘Penguin’ published a series of classical novels, among other novels.

There was just the publisher’s name, the title, the author, and an image of a penguin on the front cover (see left.)
It could be that back in the days when Penguin books flourished, there was no need for ‘fancy’ book covers because people were so desperate to read a good book that the cover was irrelevant.
The reason they were desperate to read a good book was probably because there was only a limited supply of good books available.
Self publishing has changed that; there are now plenty of good books available.
This might explain why it is necessary to have a good book cover.

Articles in the ‘My cheap book cover design for self publishing experience’ series.
My cheap book cover design for self publishing experience part 1
My cheap book cover design for self publishing experience part 2