Amazon offers its Prime members the American Girl Mini Kit Doll with Mini Book
for $16.31 with free shipping. (Non-members can get free shipping on orders over $25; otherwise, shipping adds $3.99.) That's the lowest total price we could find for any American Girl doll by a buck. This 6.5" mini doll comes with a 3" "Meet Kit" book.
Update: As a reader discovered, Walmart has it for $15 with in-store pickup via Site-to-Store. (Shipping adds $1.97.) Sales tax is added where applicable. Of note, Walmart also has an assortment of American Girl Mini Dolls starting at $14.40 with pickup.