If you own a domain, which you do, you can get wildcard certs from Let’s Encrypt using a DNS challenge. Most (all?) popular reverse proxies can do this either natively or via an addon/module, you just need to use a supported DNS provider.

Make an offer of $0.01. Assuming the responses aren’t automated, every time they reject it, raise the offer by 1c. Keep doing it till you hit the $15 mark and then just stop. It could waste literal years of their time.