Hi Josie, great question. To work out how much to spend you really need to do two things 1: Set yourself a goal and 2: test how your adverts perform. For example, if your goal is to get landing page views on your website then run a test camapign with a smaller budget ($50-$100) and at the end of the campaign analyse how many landing page views you got and what the cost per view was. If it cost you $1 per landing page view then you can budget approximately $1000 to reach your goal of 1000 views.
Of course there will be variables – often ad camapigns will perform better at certain times so you need to factor in a contingency.
You also need to remember that you should always be refining and optimising your adverts to bring the average cost down. That means that ideally you’ll get more for your budget over time
It’s also important to think about which goals are actually going to grow your business. For example, you could have a goal to get followers and spend $2000 on a followers campaign which grows your page by 1000 followers (for example). But, the average organic reach of a Facebook post these days is just 5% so you’ve just paid $2000 to show your next organic (unpaid) post to only 50 people.
Instead, you could use that $2000 to drive traffic to your landing page, encourage messenger interactions or sell products which is likely a much better use of your budget. Setting a goal that makes sense is a big part of this.
I highly recommend the Facebook Blueprint course as a great resource to help you with your Facebook advertising. https://www.facebook.com/business/learn