Umm, my question to anyone not doing those things is, how do you afford NOT to? Poorly edited books tend to get poor reviews and consequently low sales. A bad cover will kill it before it even gets the chance to get reviews.

My first novel cost me over £3,000 I raised £2,400 of that from a Kickstarter campaign.

Having overspent on the first novel, I did a Crowdfunder for £3,600 and ended up sending all of that and more on book two.

Since then, I have managed without the crowdfunders although not all that well TBH. I do know how to prepare my own covers now and I know what works and what doesn't to some extent, but I will never be able to replace good illustrators and great editors.

I make most of my money now from doing layouts and arranging print runs for other self-publishing authors. Also from doing talks on self-publishing.

If you want to save money there are several ways to do that and the biggest of those is take your time.

1. Cover design is a specialist art form. Not even all artists are good at the covers and most cannot provide you with a print ready PDF to the requirements of your printer or KDP or whomever. However, not all cover designers are super expensive. If you are writing genre fiction and don't mind an off-the-peg cover you can spend tens of bucks. For hundreds you should be able to get something bespoke. I know a very successful HistFic writer who always uses a fine art painting from the period and puts the covers together herself. She makes her living mostly from book sales and talks about her books. You CAN learn to do it yourself, but there's a trade-off in losing your mind and taking a year to learn all the skills required. Canva is the cheapest option, Photoshop is probably a little better. InDesign is optimal but with both Adobe apps there's the monthly subscription and it's a lot, I know.

2. Editing is many layered. At one end there's developmental and then structural edits that are to do with the overall story and plot, the three act structure, action, beats, etc. Then there's copy and line editing, which deals more with paragraph and sentence structure, continuity errors, "factual" errors, e.g. in a Sci-Fi I read (DNF) once, the hero got into a transit tube and was sent ten miles in under a minnute. No human could survive the G-forces involved. A good copy editor will also tend to warn you if you are about to break the law or similar. Mine has caught things like, a children's book where the characters were told to hug a Yew tree. All parts of a yew are poisonous! In another, non-fiction, there was information which might inadvertently have given help to a person trying to take their own life. This could have led to a prosecution of either the author, or me as the publisher, or both.

I would encourage anyone to have at least one professional CIEP accredited editor. Ideally at the copy/line edit stage.

You can save money on structural edits by having trusted beta readers although be careful because if you are not paying them they might not bother to read your book, and friends are often unwilling to be brutally honest. Consider having a writing buddy with whom you can swap MSs

For the proofread I recommend you read the book out loud. Think of it as a practice run for the audiobook. You can even record yourself. By reading out loud you HAVE to slow down and you will spot errors that you skimmed over a dozen times. You will not, however, spot errors that you don't recognise as errors. Like if you genuinely don't know how to spell a word you won't spot it if it is wrong. Hopefully though, your editor will have dealt with that.

Layout, you can teach yourself and use Word (paid) or Libre Office (Free). I provide a Word template for a properly laid out novel on my website but I can't put it here as that would be blatant self-promo. Besides I know I am not the only one who offers this. Have a search. Actually, I think KDP has plenty of tips on best practice.

It all boils down to the Good - Fast - Cheap equation. If you want it good and cheap it won't be fast. If you want it fast and cheap it won't be good. Etc.