Adult Coloring Books (Downers Grove/Darien border)

Seeking adult coloring books for my elderly mother. Finally got her to try coloring, & now she does it all day! Happy that she has an activity she enjoys, but she goes through a book every couple days & can't afford to keep buying them, even at the dollar store (both of us are disabled/ live on SS, & both have high cost chronic medical conditions). Would be most worth our effort if someone has multiple books instead of making trips for single books. Thanks in advance.