How to set a discount for items in a shopping cart (custom) that is not linked to an order?

Question

1C-Bitrix

Given: A
page on which the user
can fill his cart
using the quantity change controls.

Those. in fact, this is not even a basket, but some kind of emulation of it.
However, on this page you need to display the current amount in the basket, taking into account discounts.
Actually, because I did not use a standard basket.

What is the best way to manage the mechanism for setting the price?

Approximate logic:
There are sets with a fixed cost. These kits list the catalog items with their quantity included in the kit. The price of each element in the set is 0 rubles, i.e. The customer only pays for the set.

There are goods that can be bought separately from the kits (the price is arbitrary - 100 rubles).

If the user enters the number of an element equal to the number of this element in the set, then the price is 0 rubles.
If there is more than the number of elements in the set, then the price of each element is equal to the retail price (100 rubles per piece, except for the quantity that is included in the set).

Preferably use D7.