Or make them pay something towards the cost of those public spaces. Which is what the city is doing. I don't think $1 per bus per day is enough though really - it seems so obviously a token amount that I'm sure its going to go up.
It is $1 per bus per stop. Basically, every time a bus pulls into a public bus stop, they pay $1. So at a minimum that will be $2 a day (pick up in the morning, drop off in evening). But I believe buses make multiple stops.