sum of a list of decimal number field by contextual filter

Hi, I have a complex case that need anyone help.

I want to sum of a list of decimal number field by contextual filter. The structure is like this:

Taxonomy: Budget Type

Content Type 1: Budget
- Term Reference: Budget Type
- Decimal Field: Cost

Content Type 2: Application
- Entityreference field: Budget
- Decimal Field: Apply Cost

For example:
There are 2 Budget Type terms, named "Marketing" and "Operation"

There are 5 Budget nodes, named B1, B2, B3, B4, B5, with different values of "Cost"

B1, B2, B3 => with term "Marketing"

B4, B5 => with term "Operation"

I want to create a rule that when saving a new node "Application" with 'Apply Cost" and "Budget" (e.g. B1) field data, it can check against whether it exceeds the "Sum of all Cost from the same Budget Type, i.e. B1 + B2 + B3)".

How to achieve this??

Thank you in advance.