Airvasia, lion air, sriwijaya, citi link all cheapish, but you need to be lucky. Air asia is cheaper if you book way in advance or they have a sale but tickets cannot be changed and they charge for pretty much everything. Lion can have low prices but are often late. Sriwijaya are good but limited in flight times depending where you want to go. Citi link are good but limited and are owned by Garuda. There is a new kid on the block, batik air which is owned by Lion but don't know much about them.
Follow Air asia on twitter and they will tell you when the sales are. I have flown to Bali with them for 200k one way so there are deals to be had.