I like the Wally World Remy Promo loads. Not for the dirty loads that are in them but for the hulls.
In December they were $16.99 for 4 boxes or 100 rounds
Since I bought 400 rounds, it will be a while before I burn through all the hulls.
I can usually make 400 hulls get me through a year of sporting clays reloaded up to 6 times.

The expensive part is the reloading...particularly lead shot.
Chilled magnum shot is $65 for 25#'s or about $4/box of loaded shells for 1 oz loads not including the other components.