it's not just $$ that you need to save carefully but even those lockpicks are hard to find to open up all the safes and secret rooms...some safes require 5 lockpicks...even exploring every inch of the map makes completing everything almost impossible...is there a free roam option after you complete the game?
I open all safes (and what a let down, in terms of loot, what are they thinking not putting some infusions in there) and still have plenty of lock picks left. Usually carry around 20 at any time. They are pretty abundant if you look around.