Your school may have discretionary funds some of which could be budgeted for future school visits. Many educators write grants to obtain funds to cover several school visits within the year. To see a sample of state grant information click here. For instance application can be made for Grants for schools in Kentucky. Other educators hold book fairs every year and use the proceeds to help fund school visits.
Preparation is always the key to success.
Make sure the students are familiar with the published works of the Author or Illustrator. Doing this will almost always assure that significant questions will be asked and the students will be more focused for the presentation. Most Authors and Illustrators will gladly autograph copies of their books. You may want to contact a local bookseller to see if they would support a booksigning at the school. The bookseller would order a supply of the published books for purchase by teachers and students.