Even if the DDoS wasn't caught by Cloudflare, the total cost for 192TB bandwidth on Hetzner would be €172. Although even after 10 years on Hetzner I've never paid for any bandwidth, always well within their generous 20TB free bandwidth.
They also likely drop any charges if you escalate via support in case it was actually DDOS. E.g if you normally have 100GB / month and now you magically have 50TB / day.
What Netlify does is a scam.
I prefer to keep my App's stateless and running in Docker containers which means storing all uploaded files and generated assets in R2 managed storage - which is also used for Litestream backups of our SQLite databases.
Blowouts are minimized when using low cost services, e.g. we had a rogue process that ended up causing 1.5M writes to R2, which only ended up costing us $4.50 in that month.