Code Example 1:

declare @nonGA float

set @nonGA = (select sum(balance) from elaborate_query)

select sum(balance) + 0.33 * @nonGA from salary_query -- tech salary and related
select sum(balance) + 0.67 * @nonGA from oe_query -- other expenses

Code Example 2:

set @nonGA = (select isnull(sum(balance),0) from elaborate_query)