You tell them you don’t work for $500.

Or you tell them that you do.

Per hour.

But since they’re clearly such great mates with dad, you can cut them a deal.

You can also just spend $10 on a domain name with a registrar that offers dynamic DNS. Offhand, both Namecheap and Cloudflare do. I have no idea what my public IP address is because my router just updates it automatically for me. Plenty of DDNS desktop clients around if your router can’t for whatever reason.