When you are close to finishing your book, one of the things you need to take into account at all times is the inclusion of illustrations. By default, images created by a professional artist or illustrator will bring more value for your book, so do try and insert images into your book at all times. But, how can you find the illustrations you seek at a good price?
Update: After re-reading this article that I wrote a few years ago, I really feel like I should point out that homemade sincere illustrations are by far the best! What I mean is, when the author, no matter what artistic skillset, does their own artwork, it is awesome! Not only does it represent what the author (you) intended, but it has the character that every book should have. There is no shame in hiring a professional to ‘clean up’ the artwork and get it ready for print. The image to the left was done for one such an author. She had roughly drawn stick figures of the boys and I created the print-ready high-resolution image you see today. I am certain that I would not have thought of little things, like the boy grabbing the blades of grass with his toes or the home sweet home sign over the door. I cannot stress enough, these little details add to the character and sincerity of the book as a whole. Without them, some of the spirit of the book goes missing as well.
Before you start contacting any children’s book illustrator or any other professional for that matter, you need to determine the illustration types that you need for your book, the time period that your book has and its concept. Some illustrators will work only with a specific topic or theme, so this will help you narrow them down in order to get the best images for your picture book.
Once that is done, a good idea is to create a sketch or at least write down the ideas you want for your illustrations. It’s a very good idea to ensure that you add the best possible images here, so because of that try to insert images that people can easily relate to and which are relevant to your written piece. Even a few sketches are enough for an artist to figure out what you need to express, and he will take the idea from there in order to bring it to a whole new level. Make sure that you come up with multiple ideas at this stage.
The next stage requires you to pick three of the drawings that you like the most. The main idea here is that you have to focus on the best three that you like a lot, as these should be included in your book. Do remember that a book needs to have appropriate drawings so ensure that these suit the style of your book because you do want a good, cohesive product!
At this point, you need to research and find the best illustrator for the job. All you have to do is to go online and find 
the perfect illustrations that suit your needs.
Through this website, I provide high-quality kids book illustrations at an affordable price. However, I am not the only illustrator in the world and you have so many options. Here are a few ideas;
You can go to your local art school and talk to the administrator or even post an ad. Students can be very talented and work for a reasonable rate to build on their portfolio.
Another option is to join a local author/artist group. I have been in a few and they are a great way to get constructive criticism on your work and be introduced to talented local artists.
There are also many talented artists available online. I wish you and your book the best!