What are your most difficult sites to scrape?

What’s the site that’s drained the most resources - time, money, or sheer mental energy - when you’ve tried to scrape it?

Maybe it’s packed with anti-bot scripts, aggressive CAPTCHAs, constantly changing structures, or just an insane amount of data to process? Whatever it is, I’m curious to know which site really pushed your setup to its limits (or your patience). Did you manage to scrape it in the end, or did it prove too costly to bother with?