I have just returned from Manado. When I entered I changed sterling into IDR at the airport. Big mistake rate was 17,200 IDR to £1.00. Later I change at a local exchange and received 19,000 IDR to £1. Lesson - ask your driver to stop at an exchange it will save you money.
If you pay by credit or debit card you will receive a better exchange rate but most charge a fee for using the card.
Hope that you find this useful.