It's set mostly by supply and demand across the market. The owner and the renter can get together and negotiate a small deviation based on the property's idiosyncracies, but it's the market that's primarily driving it.
Like many US markets, local rental prices have ~doubled in the last two years. As in every case of price gouging, sufficient supply would have prevented the opportunism that is presently causing broad harm.
Huzzah for supply and demand, I guess.
Increase the supply through deregulation or incentives and we won't have this problem.