It depends. The "average" power consumption of a 19" standard res raster arcade cabinet running either florescent marquee or LED is about .9a to 1.2a at the high end... vectors suck up a bit more coming in at close to that 2a mark.... and the only 19" raster arcade game I've seen hit 2a are Atari medium-res games (paperboy, etc)...
The only way to truly get a good idea would be to measure the games you have with a kill-a-watt device. If you're looking for a ballpark estimate, I'd venture to guess 2a per cabinet is a good "ballpark" guess based on a mix of 19"/25" raster/vector mix...
So I'd tell your friend 100 games would use about 200 amps of power.
I measured mine a few years ago - around 45 games in my basement, with a mix of classics, vectors, newer stuff, drivers, and pins... it was about 80A with everything running.