Play group is cheap. Ours is run by a church and costs about $30 a year + $3 a week for craft expenses and tea/coffee.
Parks, museums, library, places like south bank (get the bus/train), take a packed lunch.

Food wise I found a good cheap fruit shop.
Buy the same things from coles each week so theres no suprises at the checkout.
No extras unless they're budgeted for. Not even a chocolate bar because they all add up very quickly.
Take food to the shops so I dont end up buying takeaway/snacks for DS.
And we are vegetarian. Theres lots of yummy vegetarian dishes, and many meat dishes can be changed to vegetarian by switching a few ingredients.