After doing some research online, there was some ambiguity regarding the visa-on-arrival for Indonesia, so I hope this clears it up.
We travelled into Bali in February 2015, so here is some up to date information.
The visa on arrival costs $35 USD per person and is good for 30 days. The first day out of your 30 is the day of entry, and the last day is the day your flight leaves. If you go over the 30 days, you will be charged 300,000 rupiah ($30) per day. You can extend your visa for an extra 30 days (for a total of 60 days) once in the country using a tourist office to do so.
The following applies for Denpasar (Bali) Airport only:
You will see two separate queues - one that says "Immigration" and another that says "Visa on Arrival". Make sure you get into the VOA queue before heading to immigration, as we saw many tourists follow locals who do not have to purchase a VOA straight into the immigration line who were then turned away.
I recommend you have the cash for the visa on arrival in USD. It is $35 USD, however, if you wish to pay in AUD, rupiah, GBP, or other currencies, you get ripped off (bad) on their conversion rate. In February 2015, the cost for the VOA in rupiah was 450,000 ($45 USD), so right there you lose $10.
Lastly, Visa and Mastercard credit cards are accepted at Denpasar (Bali) airport for the visa on arrival. Despite this, the line moves a lot faster if you pay in cash, so for timing purposes, I would recommend you pay in cash.