Did a family camping trip, and while it's certainly cheaper than say flying a family of 4 to some corporate money extraction theme park i wouldn't say it's cheap in absolute terms.
To start you're going to need some gear: Tents, sleeping bags, tarp, axe, camping pads, cooler, camp stove (debatable, you could do cold food and cook a meal or two on the fire), etc.
There are reoccurring costs: Any camping specific foods (s'mores :D ), ice for the cooler, gas to drive there, propane for camp stove, wood for fire and the big one is campsite fees. The state parks here are $25-$35 a night. So for a weekend trip of 2 nights figure $60 in site fees, $30 in food and supplies, $15 in gas, $20 in wood (unless your car isn't packed to the roof and you bring your own, not in our case) and you're at $125.
Again, I'm not bitching excessively. Everyone had a great time. But up front costs can be fairly expensive even if you shop around or go thrift store and it's not free to pitch a tent.
Comments or tips?