There are loads of cheap flights to Bali from Jakarta and other smaller Indonesian cities.
There is a choice of various domestic airlines that change their names as fast as you change your underwear.
The only two airlines my girlfriend and I like to take are AirAsia and Lion Air with a young fleet of aircrafts, good safety records and cheap prices.You can even book tickets online, which makes it very convenient when you’re not in Indonesia yet.
During the Christmas high season we paid around IDR 700.000 one-way Bali-Jakarta, which is around 50 Euro’s or 70 USD. In the low-season flights to Bali with AirAsia or Lion Air are much cheaper.
We often pay around 30 Euro’s/50 USD. Pretty cheap for a two-hour flight right?
These tips are of course based on my own experiences. I can imagine that there are more.