Then pad the bill a lot of misc other nonsense: social media liability insurance (yes this is a thing), ARIN fees, LLC registration, a literal fax machine (for DMCA compliance), monitoring, etc. Grand total will hover around $1000.
Architecture is a core + CDN model. The main servers run as a HA cluster in a datacenter, and then the anycast CDN caches content at the edge. It's not too far away from how S3+Cloudfront works or something like Cloudflare works. Nginx does all the heavy lifting, and the "front store" is just a giant blob of ruby: https://github.com/neocities/neocities
Not too bad for 110,000 web sites. Costs at this point are pretty stable for the next million sites (but surprises happen). I can double our bandwidth capacity for about $200/mo in less than a few hours if I needed to in a pinch.