What would this have costed had they used render or railway? Maybe, what, $200 a month?

Vercel's pricing is so ridiculously convoluted that you can't even cleanly compare usage. With render/railway/(insert provider of choice) you can at least predict that you're your biggest cost is going to be egress.

edit: I just saw that it gets 450m pageviews. I'm guessing on the upper end this costs ~$1k with railway + cloudflare?