On Bali, especially in the Kuta/Legian area, you'll have no problem finding an ATM, it seems there is one every five meters.
They usually have some kind of a limit on how much you can take out. The limits are about 1 or 1.5 million RP. (US $105-$170). I found one in Kuta that let me do 2 million.
The only problem is that sometimes they spit out 100,000 rupia bills, which sucks because you need small bills to bargain for taxis, clothes, sunscreen etc. You'll end up losing money because people can't make change for 100,000 RP.
There are shitloads of banks in the Kuta area, I took out cash advances for 5 million. Five Mil lasted me about a month and a half. My bank charged me US $5 each time I used an ATM, so instead of using ATMs, I did large cash advances.
When are you going, how long will you stay? I need to go back soon. Lucky.