How much should you spend on ads?
The short answer? It depends, but usually at least $2k/month for 2-4 months.
We recommend allocating at least $2000 per month on ad spend when you're running a Facebook ad campaign and to anticipate it taking at least 2-4 months of testing to find the best results. With that said, there are MANY factors that affect your ads -- including but not limited to your website foundation -- so it's impossible to guarantee that that amount of time will apply to everyone. For some it takes less time, for some it takes longer. The fact of the matter is that if you have major hangups in your funnel, such as a low website conversion rate, you're not going to reach your ideal metrics with your Facebook ad campaign UNTIL you address that website hangup.
One thing to keep in mind is that you DON'T want to throw $6k into ads your first month (instead of $2k each month for 3 months) and expect that to give you all the testing data you need. You can't rush testing. You need to give FB's algorithm enough time to settle in and optimize. FB ads can be a slow and long process....definitely not overnight.
What if you can't afford $2k/month? The reality is, we've seen FB ad campaigns immediately take off and hit their ideal metrics with a mere $5/per day. With my husband's guitar teaching business, we always kept super low ad spend...often just under $500/month, but mostly around the $250/month mark. But this is the exception, not the rule.
If you're strapped for cash, that's OK. You can still run ads at a low ad spend and get an initial gauge on what's working and what's not. This will give you some low amounts of traffic which can help you figure out what needs to change site-side too. This is best done on your own, essentially to get your feet wet. We, (and most advertising agencies), require a minimum $2k monthly ad spend when we manage your ads. The reality is that level of budget allows us to effectively test. Without it, it makes our job much harder and, really, all we want is to see you succeed...so we don't want to impede our efforts.
If you're in the position where you can't afford $2k/mo and want to get your feet wet with ads, your best bet is to use expert FB ad guides to help you DIY.