Select average from MySQL table with LIMIT

I am trying to get the average of the lowest 5 priced items, grouped by the username attached to them. However, the below query gives the average price for each user (which of course is the price), but I just want one answer returned.

SELECT AVG(price) 
  FROM table 
 WHERE price > '0' && item_id = '$id' 
GROUP BY username 
ORDER BY price ASC 
   LIMIT 5