Google has $100,000,000,000+ in the bank and slightly more than that in revenue last year, so realistically if they need 100,000 more employees to handle this they will still be ridiculously profitable, especially when they call them contractors to avoid health care, and evade taxes on a global scale, and woo oppressive new markets like China.

Charging users to upload videos would solve the problem.

I doubt ISIS and the like lacks funding. If this is really what you want to prevent money wont be a big barrier.

You're not thinking laterally. The problem isn't extremist videos. The problem is that there are too many videos uploaded to reasonably check all of them. Charging would solve that problem, which in turn solves the problem of extremist content.