Yes, when you file an arbitration against a company, regardless of how legitimate your filing is or how likely it is to be thrown out of court, that company is out at least $1000. If you wanted, you could pull together 10,000 HN users to file arbitrations, and HN is going to be hit with a $10M hammer regardless of whether there is any legitimacy to the claims.

I believe the amount varies state to state, but is generally over $1000