The good news is you can control your budget and fine-tune your demographics when advertising on Facebook. You can spend as little as $10/day, but advertising on Facebook alone may not get you far. You should look at a range of book marketing avenues. First, here’s our guide on Facebook Advertising, and a look at Facebook advertising costs. Next look into Instagram and other social media marketing options. If you’re publishing this as an eBook, you should consider self-publishing on Amazon, too.
I hope this points you in the right direction. Good luck with your book launch!