Filtering by window function result in Postgresql

I don’t know if this qualifies as “more elegant” but it is written in a different manner than Cybernate’s solution (although it is essentially the same)

WITH window_table AS 
( 
   SELECT s.*, 
          sum(volume) OVER previous_rows as total
   FROM stuff s
   WINDOW previous_rows as 
        (ORDER BY priority desc ROWS between UNBOUNDED PRECEDING and CURRENT ROW)
) 
SELECT * 
FROM window_table
WHERE total < 1000
ORDER BY priority DESC 

If by “more elegant” you mean something that avoids the sub-select, then the answer is “no”