We went to haven last week and we had a lovely time.
We spent £400, that was including petrol (but we only lived 2 hours away) and we took cereals for breakfast, a bag of apples and a multipack of crisps, we also took a bottle of squash and the kids juice bottles. We had breakfast every morning in the caravan, we packed crisps and apples for snacks and we took our own drinks when we went for walks etc.
We had a meal out every day, but we had a meal in too. So if we had lunch out we had dinner in.
We took full advantage of the childrens activities that were free, and the swimming! We also paid for an "activity pass" (the 6 sessions one) and the older two sprogs got 3 sessions each to choose. That was £38 and i think well worth it!
Hope you have a fab time x