Assume it was 1-click and 100% automated to deploy, run and update a Hub.

How much per month would you be willing to pay to run one? 

No direct economic incentive other than you know you're supporting Farcaster decentralization and you have your own copy of the network.

OK, if you're answer is you wouldn't run one.

As a user I'll pay $10/mo if the social network is high-quality, no bots, interesting conversations. Then if you pool these payments together and distribute to node operators, and I can see a graph that shows "Decentralisation Factor" (aws, gcp, etc), I'll be continuing to pay to keep the network up an decentralized.