In Dynamics 365 (D365), how do I set up a fixed sale price for a product when a specific quantity is purchased (not tiered)?

Question

Hello. I have many items that we currently cannot place in a BOM because they are drop shipped directly for the vendor. This makes it challenging to sell a multi-pack of a single item at a discounted price without manually discounting each unit or taking a larger discount off of the total. Currently, we assign an item number to the single product SKU and multi-pack SKU (note: the multi-pack item number is simply for identification as we cannot create am actual BOM). I assume there is a way to set up a trade agreement journal to do this, but, again, I am a novice and newly introduced to D365. I know we can enter tiered pricing, but I do not want tiers. I am looking for a single fixed quantity that would give the customer a set price every time they purchase that quantity. Here is an example of what I want to do.

Example

Single Item: #12345 Red Truck Single, Retail Price $10.00, Drop ship from vendor

Multi-Pack Item: Red Truck 10-Pack, Retail Price $90.00 --> This is quantity of 10 units of #12345 above. If the customer purchases 10, they pay $90. If they purchase 20, they pay $180, and so on. I do not what a quantity of 11-19, 21-29, etc. to discount the price.

I am just looking for the simplest way to do this, whether by journal, BOM, or other method, without causing issues for accounting and/or purchasing.

THANK YOU!