A friend of mine just suggested a great and affordable family vacation for this summer: YMCA summer camp. Check out www.ymca.net/find-ymca-camps to locate a camp in the state in which you are interested.
One camp that comes particularly recommended is Trout Lodge & Camp Lakewood on Missouri's Lake of the Ozarks (just 90 minutes south of St. Louis). The per person rate includes three buffet-style meals a day, and you can choose from loft suites in the Trout Lodge or family cabins. (Note that the rooms do not have phones or TV's, so you will REALLY be getting back to nature. Wonder if TJ could survive without watching at least 10 minutes of Sesame Street a day??)
The accommadations are reasonable - suites (which have two roll away beds on an upper level and two queen beds on a lower level) start at a base rate in the summer of $169 (that is for one adult - each extra adult is $59, ages 6-17 $49, and ages 5 & under free). The family cabin includes two bedrooms (each with a full bed and two bunk beds), two roll-away beds, and a crib and the base rate is $299. Most activities are free of charge, (although a few of the more exotic ones are a nominal cost like $5 per person) and include things like archery, boat rides, cave exploration, fishing trips, swimming, mini golf, nature hikes, sand volleyball, and ping pong. Arts and crafts are also provided.