Referencing a relatable but differnent price class

I am developing a GI where I need to change pricing of items on sales orders based on customer price classes. 

For example: 

If a customer has a customer price class of CUSTOMER, I need to reference the price of an item associated with COMPCUSTOMER. COMPCUSTOMER will never be a customer price class that we actually designated to a customer, but it’s more of a reference.  I’ve been trying to create a reference GI for my main GI to use but because you can’t use formula fields as relation link I’m a little stuck.