This is a craft that has many thinking it is easy. Take a look at what goes into a good picture book.
It will be under 1000 words. Perhaps, if it is really polished it will be 500 words or less. Each word must be chosen carefully and must belong to the story. Because picture books are usually read to younger children the type of word does not need to be "readable" by the child. But with the combination of words and great illustrations, a young child can "read" the book to him or herself after hearing it once. The words may not be the same but the essence of the story is there and the pictures lead the child from page to page and event to event.
If the author has read their book to their family, children in the neighborhood, their own children or grandchildren and everyone "loved" it, there is still more to do. Maybe it is a great book. Maybe not. The advice many illustrators will give is to submit the book to a traditional trade book publisher. Yes that may mean rejections, long waits, and disappointment. But, it is really the first step that should be taken. The author does not need to submit illustrations with the book unless they are also a professional illustrator. The job of choosing an illustrator for any book is the job of the art director and editors of the publishing house. Some few houses will allow an author to request or suggest an illustrator, but that is up to the editors not the author.
Some authors really do want to self publish. If they do, then there needs to be a reality check.
Some will choose a Print on Demand book publisher. This usually drives up the price of the book in order for the author to make a profit.
If they are using a printer who prints many books at a time, they will most likely need to commit to at least a run of 1000 books. The price per book is small, but there is shipping and storing to be considered. And still the author is not done with the self publishing process. There is marketing to be considered. How this is done and whether a PR firm is hired will determine the cost of marketing.
Once all those costs are considered the price of the book needs to be determined. Too high and it will not sell, too low and the profit margin is dismal.
If truly determined, truly talented, and all of the above are considered carefully the self publisher is still not ready to launch their book. Why?
Because there needs to be one more element in the process. A good editor, proof reader or professional needs to take a look at the manuscript. It may be hard to do but words will most likely have to be sacrificed. Scenes may have to be truncated or moved around. It might be a really good idea to put that manuscript away for a month or more and come back to it with fresh eyes and see if improvements can be made.
There is magic in a picture book that holds the attention of a young child and appeals not only to them but to the adults that may have to read that same story over and over, night after night. That's what you want from your picture book?