Is there a cost for an appointment/missed appointment?

No. Appointments are free, with no commitment to purchase aligners. There’s no fee for missing an appointment.

That said: If you do miss an appointment, you’ll have to live with the mental image of us staring sadly out the window, wondering what went wrong. Was it something we said? Something we did? And so on and so forth, hour after tortured hour, until our long, lonely, umbrella-less walk home in the rain. So there’s that.