Split revenue line with SLA and derive amount based on Item cost

Summary:

We have scenario wherein the revenue line is to be split and the total revenue amount is to be broken down based on Item cost and Mgmt Fees

Content (please ensure you mask any confidential information):

For example:

For a Revenue of $100

A/R Trade A/c Dr.$100To Fulfillment Revenue Cr. $80 (Item cost * Qty = $8 * 10)To Mgmt Fees Cr. $20 (Fixed Fee * Qty = $2 * 10)

Any suggestions if this can be achieved via SLA at AR Invoice level? How to access Item Cost (Inventory item with actual cost method) when defining User-Defined Formula?

Or is there any other way to manage this scenario?