Stopped by Academy today and saw 5-round boxes of Rio Royal 00 buckshot for $2 each. From what I have read, it seems to be a pretty decent budget buckshot load.
http://www.academy.com/shop/pdp/rio-game-load-royal-buck-9p-12-gauge-shotshells/pid-844053
http://www.academy.com/shop/pdp/rio-game-load-royal-buck-9p-12-gauge-shotshells/pid-844053