How much does it cost to market your book?

I have been researching the internet trying to find an answer to this question. And the answers are across the board. I've read $20,000 up to $50,000. I ask the question because I need to have a foundation and an end point. I'm trying to be realistic. I believe a lot of indie-authors/publishers have problems because they think writing a good book is enough. But I believe there has to eventually be some form of paid advertisement. They say the best advertisement is word of mouth but that's not free either. Here's the financial breakdown for my "word of mouth" campaign. I did the math and so far my budget has come to a total of; let me see here------gettin' my calculator-------hold on, almost done--------$191.00. Let's break it down, shall we: $40 for 10 books for blog giveaways $25 for postage $98 for a two week Facebook Ad campaign $28 for a two week Goodread Ad campaign My budget is $5000 which is a loooonnnnggggg way from the minimum of $20,000. How did I come up with the $5,000 number? According to sources, that's usually the average a first time author will receive for an advance. My focus is going to be how to spend that $5000 wisely and make it stretch to the four corners of the globe or just Illinois.