They are pushing about 245 Mbps out of Cloudflare (averaged over the month). Wholesale IP transit prices are anywhere from 10 cents to a dollar per Mbps depending on volume. Cloudflare dumps 40% of their traffic over peering, putting their price at $14.70/mo. Ignoring fixed capex of servers, Cloudflare is making about $25/mo on this customer.
Given the $11 Backblaze bill, I estimate about 2 TB of data.
A capable dedicated server with 2 TB of disk and 1 Gbps unlimited bandwidth will run about $30 in a major European metro, maybe double that for the US.
With a grand total of $370 vs. $60 worst case, they are spending 516% more to be "serverless."
Edit: Yes Cloudflare has more than one server. Double the price and put one in the US and you still come out ahead.
Edit 2: I'm not saying one way or the other is better. Just that the title is very clickbaity for a "put a credit card into a website" payoff.