The average sized ATM can hold as much as $200,000.00 in cash especially during business hours but during hours that the bank or business is closed the ATM usually only holds at most $10,000.00 or even less in cash.
So yes stealing an ATM can get you a lot of money if successful but totally not worth the risk since most ATM machines are hard to break into once you steal them and they also contain GPS tracking devices to track the location of the ATM machine.
The ATM machines that are located outside banks tend to have the most money in them but the ones in the stores usually have less cash in them.