This is a hard question to answer. If you have a tight budget there is ways that you can publish your book for almost no cost. On the other hand you could spend thousands of dollars getting a book published. So lets break this down.
There are three main things when it comes to self publishing a book that you will/can spend money on. Book cover, editing and marketing. Each of these things can happen at different price points.
If you are somewhat tech savy you can create a cover yourself. I know that a lot of author and people will tell you that’s a horrible idea. But you know what is a even worst idea? Spending $1,000 on a cover for a book you don’t even know is going to sell. All you need to do to create your own cover is buy a stock photo which could be $30 or so and use that to create your cover. You can do this on photoshop, pages, or even directly on Amazon. It’s really up to you but try to make it as professional looking as possible. Look at other covers in your genre and see what they are doing.
Another option is pre-made covers. I personally really like pre made covers. They are affordable and look very professional.
High Budget-$300 +
Hire a graphic designer. I really like Reedsy for this. You can work with a graphic designer and tell them exactly what you want. They then can give you some options. There are some author who set up photo shoots so they can make sure they have a completely unique cover.
Editing is something you do not want to skimp on and if you have any money in your budget you should spend it on editing. But if you don’t there are free ways to get your book edited. One of them is to use Beta Readers. These are people who love reading in your genre and are happy to give feedback on your work. I found my beta readers on Instagram and they are very helpful. Another option is critique partners. You can join a facebook group and swap stories with people who will give you feedback.
Medium budget-Copy editing
At minimum unless you are fantastic at grammar you should get your book copy edited. The price of copy editors vary depending on the length of your book and the editors experience. Check on Reedsy for more information.
High Budget- Developmental and copy editing
For new writers I highly suggest a developmental editor if you can afford it. I know personally it has helped me tremendously in becoming a better writer. Working with a editor is the best writing education I have ever gotten.
I think marketing is pretty self explanatory but the free way to market your book is going to be social media, blog, networking, building a team, giving out free copies, etc. More expensive way to market is paid advertising.
I will warn against spending a bunch of money on your first book. Unless you already have a big platform or a large mailing list there is no guarantee that your book is going to sell anything. Spend a small amount on your first book and you can increase your budget as you sell more copies.