Looking at the pictures you posted, I'm assuming you do not already have a field in your data with the budget values. Is this true?
If so, I think you'll want to code that in using a Budget calculated field like:
You'll obviously need to extend this logic as far out as necessary to cover all your subgroups, but this will write that total budget value to every single row in the data, based on that row's subgroup. So you can drag this field into your view, set the aggregation to AVG and then right click the axis and select Add Reference Line. Based on your pictures, I think you want Scope to be set to Entire Table, Value to be set to AVG(Budget) and and Label to be None. You can play with these settings (as well as the formatting) until you get something you like. This solution is posted in the attached workbook with some sample data.
Book1.twbx 17.4 KB