This is more of a SQL question.
Use the MIN and MAX aggregates:
SELECT type, MIN(price) AS minprice, MAX(price) AS maxprice FROM bob GROUP BY type WHERE type='$drop' AND subtype='$drop_2' AND ssubtype='$drop_3'
Which should return a result set with the type, minprice and maxprice within it. The WHERE condition is optional depending on how many records you want.