From a 2013 reddit AMA: "Each ATM is different. We do 12,500, but have ones with metal cases that reach 26k."

From a 2010 time article: "The average size machine can hold as much as $200,000, though few do. In off hours, most machines contain less than $10,000."

In the article they cite a Philadelphia theft case where a single stolen machine held $96,000.

As others replied, it varies.

In Japan, an ATM inside a bank might hold up to 40 million yen (≅ USD 350k) while an external one might have up to 30 million (≅ USD 270k).

Japan's a fairly safe country but there have been many cases of ATMs getting stolen too. Power shovel seems to be the method of choice.

The ones I've commonly seen in .AU, 20k for the thin service station ones and 40+k for the bigger mounted ones.