Perhaps they will next spend $250 on photocopied flyers and get 500 new customers. Perhaps they will then spend $1000 on a quarter page color ad in a local paper and get 10 new customers. None of these raw amounts have any bearing on whether Facebook costs $240 for getting no customers. What matters is whether there is a return in the investment for the ad campaign.
The implication that it is better to spend $240 on an ineffective campaign than spending more than $240 on a better campaign is not a reasonable comparison.
Of course the campaign was not completely ineffective. It cost them $240 to find out that Facebook campaigns did not provide a good return in their specific case. This may or may not be applicable to other businesses. Apparently GM has reached the same conclusion with $10 million in ad money. The Pizza place is smart, they were able to come to GM's conclusions for their own case, but it cost them a lot less to learn this information than it costed GM.