Consider what's cheaper, paying for Caddy under its current pricing structure or paying for a consultant to configure NGINX? If the key selling point of Caddy is that it makes web hosting easier to manage, but you can get around that cost by paying a one-off cost for someone to set up a free, high-performance web server, you've taken away the most of the potential benefits.
As a reference, you can see the current pricing structure for Caddy here:
https://caddyserver.com/pricing
Note that the limited time introductory price is still more expensive over a year than paying a consultant for a couple of days to tweak NGINX.