Instead of paying for advertising enter a book award contest
"Awards also create interest in your book, which can lead to more sales and other opportunities. A book award may cause someone to stop in their tracks and consider picking up your book in a book store. A book award can give you an edge and sometimes that’s all the difference you need to propel your book into bestseller territory. If you win you can say you are an “award winning author.” Doesn’t that sound better? Of course it does, and you get a little magic that comes from a third party endorsement because an authority says your work is worthy, and that’s priceless."
~ Scott Lorenz, President of Westwind Communications