Adding Monthly Budget to Customer Accounts

Hello, 

I am wondering if anyone might be able to help. I am trying to create a report which will show customer sales in comparison to their budget. 

Unfortunately I am not too sure how to go about this. At the moment I have two tables:

Table 1 (Orders):

Table 2 (Monthly Budget):

The issue I am having is that this creates a many to many relationship. The many to many relationship is causing issues with calculations and when pulling in certain fields it suddenly breaks the visual. I have tried applying a bridging table to the report to link the customer name however this is filtering out customers that do not have a budget and subtotals are not calculating correctly.

What would be the best way to structure the data model?  

Kind Regards,