Indonesian Rupiah is the official currency.
Here is a price list in Indonesia for reference (by 2015):
A bottle of water (500ml): US$ 0.3
A local beer at a bar/restaurants: US$ 1.8
A glass of coca cola in a restaurant: US$ 0.65
A dish of street food: US$ 1.5
Western decent meal at local restaurant: US$12
You can get IDR from ATMs or money changers. If you visit Singapore then Indonesia onward, you can have your money changed at the Changi Airport in Singapore. The exchange rate is reasonable.
Small notes of foreign currencies are not changeable so please don’t use it as tipping or shopping in Indonesia. It will be likely to be refused. Please make sure notes you bring are in pristine condition with no defects, or they will likely be rejected as counterfeit. Get the most recently dated notes you can as these stand the highest chance of being accepted.
ATMs can be found throughout the country though charges for withdrawals are quite steep. You may also contact your bank for detail instructions of daily withdrawals limit and charges.
Credit and debit cards can be used in many shops, hotels and decent restaurants.
As to tour cost, you may compare