The exchange rate of money changers / exchange offices at the airport in Bali are not the best. In Kuta, the exchange rates are good, however, as soon as you go out is often a semblance. These are professional trick-makers. I have been exchanging my money for years at one of the two BMC Money Changer exchange offices in Jalan Raya Kerobokan. These have good exchange rates, mostly cash in stock, a security service and you get a decent receipt.