Hello,
according to this document (https://support.unity.com/hc/en-us/articles/6821475035412-Billing-FAQ-Unity-Gaming-Services) we can set a max budget for any / all UGS services.
But when I try to do that for Multiplay, the settings page tells me:
The budget amount is a monthly value that will reset each month. It applies to the total spend in your organization across all projects. You can select which UGS products to include in your budget. UGS products included in budget alerts are Analytics, Cloud Code, Cloud Save, Economy, Lobby and Voice and Text Chat (Vivox). Not possible to select Multiplay hosting (not listed)
Please help me understand this 
Edit: There’s a second question from my side, regarding billing.
From link posted above:
What will my invoice look like? Will I get one invoice per UGS product or one invoice with breakdowns per product?
You will receive one unified invoice for the following UGS services: Analytics, Cloud Code, Cloud Save, Economy, Vivox, Lobby, and Relay. This bill will not include Cloud Content Delivery services or Ads/Monetization.
There will be a separate invoice for multiplay/hosting?