Pfft. That is total baloney. Disney World is a middle class experience. Camping, hiking, fishing, and picnics are the poor person's Disney.
Unless you live in one of the dryer states out west, just about everyone is easily within an hour from a lake. It doesn't have to be a National Park. There are ton of state and city lakes. Fishing and a picnic for a day is CHEAP. Most states kids under a certain age fish for free. In state fishing licenses are a penitence. Walking around or having a picnic is free. Some places have actual trails and what not laid out. Missouri has some some awesome caves.
Simple camping gear is not that expensive. It used to be you could get surplus army tents cheap, but now you can get a decent tent or $20-30 at Walmart. Splurge and get an air mattress. A few chairs and some Off and you're on your way.