Albert Hillsborough, fourteen-year-old businessman of the FAYZ, came up with the idea of gold bullets that were earned through work as money in Hunger. The plan was put into action when Lana, Quinn, Albert, and Cookie went to get the gold, which they found beneath a floor board in Hermit Jim's Shack. The gold was then melted and made into bullets. Albert created this currency when kids weren't motivated to work and decided to create the 'Bertos as a way to incentivize the kids to do so.
Howard was the one who coined the term "'Bertos" while in discussion with Albert at the end of Hunger. Albert didn't want them to be called that at first, but Howard brought it up and the name stuck.
By the start of Lies, the use of 'Bertos as currency is in full swing and they are used to buy food and other items.
A standard salary in the FAYZ is about 3 to 5 'Bertos per day and Albert once said that a meal is equivalent to 1 'Berto
Albert then used monopoly cards so that he had something that related to coins. One bullet was worth 6 Monopoly tickets.
Toward the end of the series this currency started to decline and fewer people used and mentioned it.