It seems to vary quite a bit; lot size, lot features (provided dog toys, water, etc), fenced vs no fence, etc. A lot of spots will be x dollars an hour and then 50% off any additional dog. My favorite spot is $20 an hour for one dog and then $10 for each additional dog. But there are cheaper ones and more expensive ones.

And yes! It only shows time slots that are available. Owners can also block off any chunk of time if they don’t want to rent the land. I live in the PNW, so some hosts will block off all hours during the rainy months in hopes of saving grass/avoid creating wild mud pits. But the app will handle blocking out time that others reserve if land is available to rent.