Suppose your tariff is $1000 per seat per day.
You want to take the cost of $2000 per day when booking three places.
You will need to create a discount of $1000 per day.
And she should act only when booking three or more places.
To do this, create a pricing component with the formula:
-1000 * [INTERVALS]
And set the constraint of the action of the component - from three shares.
When booking one or two seats, the discount will not be applied.
Look at the example in action: