For the item to be considered 100% gold efficient, the aura and active would need to have a combined gold value of 256g.
The aura has a gold value of 760 for every allied champion it affects. If all allied champions are affected, the aura has a gold value of 3040, and the item becomes 199.4% gold efficient. This still does not consider the gold value of the active effect.
This item was inspired by the Iron Solari Conclave, a fan-made forum group that was named after Leona and is supported by IronStylus. Numerous other groups, led by various Riot staff members, were also formed and "warred" with the Iron Solari, but the Iron Solari were arguably the most successful.
If more than 1 champion carries this item, the buff of the aura will grant to even another carrier but cannot stack, thus if 3 champions carry this item you only gain the benefits twice once from yourself, once from the allied aura.