If you wish to offer a discount on your conference tickets, based on a certain amount of attendees signing up, you can do so by setting a rule for quantity-based discounts per billing item.
The setting can be found here:
First you start by creating the billing item, if you need help to do this, click here.
Once the detail is set for the billing item, you create the rule. If you have more than one type of discount, you just add another rule in +add rule