If you don't consider the ad management fee then it starts at $0 dollars, if you post organically on your Facebook newsfeed. Yourself. #smallbusinessmarketing
There are two options that I can go over from my own experience. If you are bootstrapping and a new entrepreneur then you must first create an optimized Facebook business page. With all the bells and whistles of optimization, to include a key word in your URL.
Once your Facebook page is up then pick a subject and a keyword that you want to focus on this first month. Post one or two sentences on those topics (not promotions) and educate your audience. This is called organic posts and over time, your ad could be seen if you have the high ranking keywords in your short content.
Do your best not to mention your promotions or reasons to call you. Try to really help your audience learn about your product. Do this 3-5 times a week. Plan to use one day, a week, to write up your weekly posts; get it scheduled in advance so you don't have to worry about it again till your next week.
Now if you don't have an audience, then creating engaging and educational ads won't make too much sense for you. This is the time to get an audience. Creating ads to get an audience will be your most important goal. This is the paid Facebook ads that can be targeted at your audience and segmented into even smaller groups.
Here we go. Dip your paintbrush into the warm water and then splash some of it on the canvas to wet it a little. Let's now dive in...
You will need to understand SEO (if you want to save money on ads cost per click) and keywords. A high ranking key word will save you money in the long run as your ad runs. Even placement of that keyword can help too. Place it at the beginning of your sentence (as much as possible) and create your sentence around that key word.
(back up, almost forgot, be sure to read up on how to write an engaging headline). Now that you know how to write headlines, move forward.
You now hopefully have a headline that evokes curiosity. And your ad gets clicks. The great news is if your ad gets clicks out the door then Facebook will thank you, indirectly, with a low cost per click. If an ad is not getting responses and is getting responses slower than molasses being poured, then expect to be hand slapped. Facebook can punish you, by charging you a high cost per click. It can be as high as $30 a click! Yep! I paid that once for a Facebook objective ad; apparently the ad was not the best.
I turned that ad off, in a quick reaction; very similar to the jump you take, when getting burned on a stove. Ouch!
Moving along, how much does it cost to market on Facebook. You will only know the true answer once you are marketing your one product or service, over time. I have found that products or services can all vary and so can the ad creation.
The lowest cost per click, I was able to get for a client that was selling an invention that was related to airlines was as low as .17 cost per click! And, if I received 60 clicks? $10.00 approx. was the Facebook cost. Not bad?
I have also managed to get another client's ad as low as .04 cost per click! So, this happened after 30 days of learning about their audience and knowing how to engage them with a headline.
Focus on your headline more than anything else. Once you feel you are strong in this area then try your luck with your content and images. Pick up a copywriting book too. It is not the navigation of Facebook that can be successful. But the actual ad writing.