When hiring an illustrator it is important to understand that you do not buy the copyright work itself, but will receive a license to use the illustration depending on the project–campaign, cover art, product design, etc. This means you as the client do not have unlimited rights because of the commissioned piece. The license usually applies only for the specific project that the artwork is being created for and can come with restrictions like the length of time, medium, size, format, location of use, and more.
Larger companies usually will want to buy and own all copyrights to the image created and pay accordingly. As a smaller business or organization, you will not need full ownership of copyrights and can save a lot of money by only licensing what you really need. If you need to acquire further rights, please let us know so we can accommodate the pricing.