Earlier quoted context omitted.
No free (or even cheap) alternatives exist. If you have a little site that might be a DoS target, you have to use it.
How many little sites do you run that get hit by DDoS? I personally run about 10 tiny websites myself, some of them have around ~1-2K daily active users, but neither of them have suffered from any DDoS frequently nor do they use CloudFlare at all. One has been hit once by a DDoS that kept trying for ~2 days to bring the site down, but a simple "ban IPs based on hitting rate limits" did the trick to avoid going down,…
It seems to me like a common misconception that you "have to have a fire extinguisher" (or other supression system), otherwise you'll have your house burn down.