When I was in Bali last week I had a little card that I carried in my wallet to help me out with prices. A couple of days before I left I made a little table of what the exchange rate was and what it converted certain amounts into such as $1.00, $10.00, $100.00, etc. Whenever I was bargaining or went to the Matahari I could easily get the card out and have a look how much things were in Aussie dollars. It was so much easier than carrying a calculator and really helped my boyfriend and myself. Of course the rate may change while you are there but its not that much of a difference, just a couple of cents!