Based on the Golden Meal offer they have in their app.
The only thing you can remove to save money from a Big Mac that saves money is the meat patties ($1.20 each). Some people add a chicken patty instead ($1.60), but sometimes all you want are fries and coke.
Since the app currently has a promotion for free medium Fries and Medium coke, one can remove all meat to get the price down to $2.60 just for the fries and coke.
You can also change the big Mac to an onion and pickle salad, with a side of big Mac sauce for free!
The price of the meat patties can vary store to store e.g. For Magill SA, the meat patties are 90c each, making the fries and drink $3.20