There are multiple safes in the game, some are harder to hack than others. There are also alternatives for manually hacking such as buying it out if you have sufficient funds (press y on the screen beforehand), and using an auto-hack device if you have one (press x on the screen beforehand).
Money and auto-hack devices can be found around anywhere like in containers, in vending machines, on corpses, and just lying around.
A relatively cheap safe to buy out is located where you fight Steinman in the water-logged area with the health machine, located on the desk in the right corner. (The buy out is $10.) Note: You can always return here as long as you have access to a bathysphere.
Any questions/comments feel free to message me or leave a comment.