Top 10,20,30 in Group
Assuming that you have SQLite 3.25.0 or later, use a window function to compute the number of a row in each sorted team:

SELECT Team,
       sum(Buy)
FROM (SELECT Team,
             Buy,
             row_number() OVER (PARTITION BY Team
                                ORDER BY Buy     ) AS RowNum
      FROM Players)
WHERE RowNum &lt;= 10
GROUP BY Team
ORDER BY sum(Buy);