We have pot luck dinners, we have them once a month at different friends houses - it spreads the cost around, and we still get to have a little bit of a social life ( we have a three month old so going out is not an option)

In the summer months we have "bring and braai's" where we barbecue, where a couple will bring their own meat and a salad and drinks. That way we only supply the garlic bread and the charcoal, which means very little cost involved.