Bali is quite cheap to visit... Just don't stay in Kuta. Travel away to these islands or to other cities which are way better. If you change $100.00 at the airport you become an instant Millionaire...you get about 1.4 Million Rupiahs.
The cost depends on where you stay and of course how many you travel with. An approx estimate can be obtained from this site.
https://www.budgetyourtrip.com/
But sometimes there are deals. For eg. once my wife booked a deal from
Datai - Langkawi - valid only Monday to Friday for an unbelievably low price for the full family, from Bookings.com. It's a luxury beach resort in a rainforest. Fabulous place. We were travelling via SIN anyway at this time and it's only a small fare to hop over with AirAsia.
Langkawi is a small island belonging to Malaysia. There are a few places to visit but activities to do. The entire island is duty free... Liquor is quite cheap but you cannot take any back to SIN. We had a lovely break and the hotel even provided me with a car for the five days, complimentary - didn't even charge for fuel.