They say they spend $12,700/month on Fastly. I guess I don't know offhand the difference between Fastly and Imgix (which they also say is their CDN), but the levels of bandwidth they're talking about are not going to be free at Cloudflare.
We serve significantly more bandwidth and requests than their 2016 numbers at under $15k compared to their $17.5k, and we're not particularly lean on infra costs being a .Net shop with Win servers and MS SQL on Azure, and I can still bring our monthly a lot closer to $10k if I can find time for some projects.
But the reality is that even thousands of dollars per month saved can take a good while to ROI against the costs of development, or more so the opportunity costs.
> the levels of bandwidth they're talking about are not going to be free at Cloudflare
Correct. Cloudflare's terms state that you can't serve a disproportionate/substantial amount of non-HTML content, so they would need to sign up for Enterprise with a full contract to get image serving via CF.
Enterprise is generally $5k+/month, but CF contracts can offer a subset of enterprise features from $500-$5k/month, so I would guess ~3k/month just to serve multiple petabytes of images. This doesn't eliminate the bandwidth costs so CF may not be the single solution for the bandwidth costs.
They specifically say they use Imgix's CDN for the images, which can be confirmed by looking at the response headers.
Fastly is used for their actual website, judging by the ASN info. Meaning they wouldn't be serving petabytes of images from CloudFlare, just HTML/CSS/JS, which should be perfectly fine.