Heii On-Call https://heiioncall.com/ has flat pricing regardless of team size.

To be pedantic, it's free for individuals / teams-of-one, so I guess you could write:

    def price_per_month(team_size)
      if team_size == 1
        0
      else
        32
      end
    end

Disclosure: I helped build it :)

EDIT: thanks to those of you signing up to try Heii On-Call! Let me know if you have any questions.