How much spending money is needed for 17 nights in Thailand, Laos & Cambodia?

I'm planning on going on a Contiki tour through Thailand, Laos and Cambodia in December and I'm trying to budget for spending money. All accommodation, flights, transfers, breakfasts, and activities will already be paid for. Basically, I'll need spending money for meals, drinks, a few souvenirs, bit of shopping etc. Answers in AUD would be helpful. Thanks!!