How I burned $10 on Vercel with only 50 daily users

I'm building discoveraiskills.com, a directory site for AI agent skills. Just launched. 50 real visitors a day. Opened the billing dashboard. $2 gone in two hours. Trap #1: Features that bill you by default Vercel has Fluid Compute (billed by CPU time) and Turbo Build (faster build machines, but more expensive). Both are enabled by default. I never turned them on. They were just running and billing. Disabled both — two line items dropped to zero immediately. Vercel's defaults are optimized for best experience, not lowest cost. Trap #2: I thought I had caching. I didn't. My site sits behind Cloudflare. Most requests should be intercepted there, never reaching Vercel. But the bill showed almost every request punching through to Vercel origin. Every punch costs money. Root cause: I was using NextAuth for login. It injects a cookie into every response. Next.js sees a cookie and automatically marks the response as cache-control: private. Cloudflare sees private and dutifully fetches fresh f