I am referring to this: https://zerossl.com/pricing

Under the section "ZeroSSL Certificates" it says for the free tier "3 90-Day Certificates" and for the cheapest paid option at 15 Euro per month "∞ 90-Day Certificates" (∞ being the infinity sign). The latter is what I currently get for free from Let's Encrypt. So to get the same kind of service, I would have to pay ZeroSSL about 180 Euro a year. Which is something I am currently not willing to do, as all my ~40 certificates are only for myself.