If you are serious about promoting your book, I will be serious about promoting it on the correct channels. I would need to understand the field of the book. If it is not one that I understand, I will pass-up on the project.
I've run social media acquisition campaigns for small and large businesses and am an intelligent marketer. Fundraising-wise, My expertise has been from corporates and foundations.
For your budget I would plan a good campaign strategy, set up a toolkit for you in terms of timeline, channels and deliverables in order that you could implement the actions yourself or hire a less-strategic (and cheaper) freelancer to implement the plan.
I'm happy to talk further.
Best, Sarah