Hmm I work in an open plan office - What if the reason we're doing so is because rent is expensive and we're a startup?
When looking at $cost_of_office_with_private_space versus $cost_of_open_plan_office it might make sense to go for the open plan office.
But $cost_of_office_with_private_space versus ($cost_of_open_plan_office + $productivity_cost) might lead to a different conclusion.
With great difficulty :)
You're right, and I think your question helps strengthen my point - the cost of office space is just one factor.