The ultimate prize of the heist is enough coins to fill two saddlebags – silver coins, not gold, which would be too noticeable. The amount of money isn’t given, but the bags are heavy enough to slightly slow the main character, who is specifically described as having bulging calf muscles and biceps. It’s also mentioned that it’s more money than an elite king’s guard will ever earn. I’m guessing it’s at most 100 pounds of silver coins – in 3e+ D&D terms, that’s worth 500 GP. This is enough money to murder or risk your own life for, even if you’re one of the highest-level characters in the city. (Of course, for picaresque characters, copper is enough to murder for.)
A picaresque campaign has to be on the silver standard, at the highest. Anyone throwing gold around is either a mark, or a con man pretending to be a mark. And that might not be real gold anyway. Remember that in literature, whenever anyone gets a gold coin, they bite it. There must be a reason for that. At least a quarter of gold is probably counterfeit.