The average selling price is $ 3.91 per unit . That 's a drop of just over two percent from May 6 . -- San Francisco Bay area $ 4.17 . The all - time high is $ 4.11 in May 2008 .
The average selling price is $ 3.91 per unit . That 's a drop of just over two percent from May 6 . The all - time high is $ 4.11 in May 2008 .