Hi, Michael! The Picnic in the Park can be purchased by visiting the podium just to the left as you come through the gates at Disney's Animal Kingdom. They will give you a receipt that you then take to the Kusafiri Bakery near Tusker House to pick your lunch up when you're ready.
There is not currently a similar meal in the other theme parks, although I have to tell you, my family so loved this picnic, that my fingers and toes are crossed that they might offer something similar in the other parks.
There are some economical options throughout the theme parks, and many of them rely on being able to share. We like the 1/2 Rotisserie chicken meal at Cosmic Ray's in the Magic Kingdom. It comes with mashed potatoes and vegetables, and we buy two of them and split it among the five of us. That makes the meal around $20 plus drinks.
The Yakitori House at EPCOT has a counter service meal for children that includes Teriyaki chicken, steamed rice, vegetable, and a kid size soft drink for less than $6, and that really is a nice lunch for myself. We usually leave there and grab a Kaki Gori shaved ice treat afterwards, so we don't want to be overly full.
Other options are buying a hot dog for everyone and splitting fries at Casey's Corner - although that will still set you back $30 with drinks. We also share the turkey legs - they are huge and one leg easily feeds two of us. We'll add a couple of fruit cups and make a meal there.
You can still have a wonderful time on a tight budget. Visit
www.allears.net to check out menus and prices and come up with a plan that works for your family.