Definitely consider St. Louis! See below for the best free activities. I've done all these free activities multiple times (except the wild bird sanctuary) and they are all good for families.
Some of the things worth paying for are the City Museum and the Magic House.
From:
http://stlouis.about.com/od/freethingstodo/a/Free_Attraction.htm
Its no secret St. Louis is one of the best cities in the country when it comes to free stuff to do. Were not talking about the small stuff youll find in other cities, but major attractions like the world-class St. Louis Zoo.
But dont forget theres also the Science Center, the Art Museum and more. It doesnt matter if youve lived in St. Louis all your life or youre new to the area, these top attractions are worth a visit.
The World-Class St. Louis Zoo
St. Louisans are very proud of their zoo. Not only is it considered one of the top zoos in the country, its free! And, as home to more than 5000 animals, each visit to the Zoo can be a unique experience. Whether youre there to see the residents of the Penguin & Puffin Coast, or to welcome new baby elephants in the Rivers Edge, its hard to beat a day at the Zoo.
Although admission to the Zoo is free, some attractions like the Children's Zoo and Zooline Railroad have a small admission fee.
The St. Louis Zoo is located at One Government Drive, just north of Highway 40 in Forest Park. The Zoo is open daily from 9 a. m. to 5 p.m., with extended hours in the summer.
The St. Louis Science Center
The St. Louis Science Center is truly a hands-on experience for the whole family. You can test your knowledge of fossils and dinosaurs, clock the speed of cars on Highway 40 with a radar gun or experience what its like to travel to outer space in the planetarium.
The Science Center is open Monday through Saturday from 9:30 a.m. to 4:30 p.m., and Sunday from 11 a.m. to 4:30 p.m. Admission to the Science Center is free, but you must buy tickets to special exhibits and the OMNIMAX Theater. The Science Center is located at 5050 Oakland Avenue in Forest Park.
The St. Louis Art Museum
The St. Louis Art Museum has more than 30,000 paintings, drawings and sculptures and also boasts one of the worlds top collections of 20th century German paintings. There are also free kid-friendly tours and activities on Sundays, and special free lectures and live music on some Friday nights.
The St. Louis Art Museum is open 10:00 a.m. to 5:00 p.m., Tuesday through Sunday. On Fridays, the museum is open until 9:00 p.m. The St. Louis Art Museum sits atop Art Hill in Forest Park.
The Missouri History Museum
Whether its the 1904 Worlds Fair, Lewis and Clark or Charles Lindberghs flight across the Atlantic, the Missouri History Museum has it covered. The museum provides a look back at key events that shaped St. Louis through the centuries, with plenty of artifacts, exhibits and other stuff to capture your imagination.
General admission is free, though there is a fee for special exhibits. The museum is open Friday through Monday from 10:00 a.m. to 5:00 p.m., and Tuesday, Wednesday and Thursday until 8:00 p.m. The Missouri History Museum is located at the corner of Skinker and DeBaliviere in Forest Park.
Citygarden
Citygarden is one of the newest attractions in Downtown St. Louis. It's a city park filled with fountains, wading pools, sculpture and more. It's a great place to do a little people-watching, take a walk or let the kids to play on a warm day.
Citygarden is located along Market Street between 8th and 10th Streets in the heart of Downtown St. Louis. It is open daily from sunrise to 10 p.m.
Anheuser Busch Brewery Tours
See how Budweiser and other AB beers are made during a free tour of the Anheuser Busch Brewery. You'll learn about the history of beer-making in St. Louis and see the technology used to brew today's beers. There are also samples for those 21 and older.
Tours are available Monday through Saturday from 10 a.m. to 4 p.m., and Sunday from 11:30 a.m. to 4 p.m., with extended hours during the summer. The Anheuser Busch Brewery is located at 12th and Lynch Streets, just south of Downtown St. Louis.
Grant's Farm
Grant's Farm is another great place to see animals from around the world. The 281 acre farm in South St. Louis County is home to hundreds of animals, including the famous Budweiser Clydesdales. A tram ride takes you to the middle of the park. From there, it's easy to explore. Admission to Grant's Farm is free for everyone, but parking is $12 per car.
Grant's Farm is open on weekends in the spring and fall, and every day (except Monday) in the summer. The park is located at 10501 Gravois Road in South St. Louis County.
World Bird Sanctuary
A visit to the World Bird Sanctuary is your chance to get an up-close look at bald eagles, owls, falcons, vultures and more. The Sanctuary is also the place to learn more about the world's threatened bird species through a variety of seasonal shows, educational programs and special presentations. Admission and parking to the WBS are free.
The World Bird Sanctuary is open daily from from 8 a.m. to 5 p.m. (except for Thanksgiving and Christmas). It is located at 125 Bald Eagle Ridge Road in Valley Park.
Cahokia Mounds
For a true look at history in the St. Louis area, there's Cahokia Mounds. This ancient archeological site was once home to the most advanced civilization north of Mexico. The U.N. has named Cahokia Mounds a World Heritage Site because of its role in early American history. Visitors can climb to the top of the mounds, take a guided tour or check out the exhibits in the Interpretive Center.
Cahokia Mounds also hosts special events like Kids' Day, Indian Market Days and Indian Art Shows. Admission is free, but there is a suggested donation of $4 for adults and $2 for children. Cahokia Mounds is open daily from May to October, and Wednesday through Sunday from November to April. It is located at 30 Ramey Street in Collinsville, Illinois.
Cathedral Basilica
The Cathedral Basilica in the Central West End is more than just a church. It is the spiritual center of the St. Louis Archdiocese. It is also the home of the largest collection of mosaics in the world. It took nearly 80 years to install the more than 40 million mosaic glass pieces that adorn the inside of the church.
Guided tours are offered Monday through Friday (by appointment) or on Sundays after noon mass. The Cathedral Basilica is located at 4431 Lindell Boulevard in St. Louis. (You can also do a self-tour when they are open).
Laumeier Sculpture Park
Laumeier Sculpture Park is an outdoor art museum in South St. Louis County. Visitors will find dozens of pieces of art spread out among the park's 105 acres. There are also indoor galleries, special exhibits and family events. Every year on Mother's Day weekend, Laumeier hosts a popular art fair.
Laumeier Sculpture Park is open daily from 8 a.m. to sunset. Free guided tours are offered the first and third Sundays of each month from May to October. The one hour tours depart from the museum shop at 2 p.m. Laumeier Sculpture Park is located at 12580 Rott Road in St. Louis County.
(The Arch) Museum of Westward Expansion & Old Courthouse
While it does cost money to ride to the top of the Gateway Arch, the Museum of Westward Expansion is located under the Arch is free. It features exhibits on Lewis & Clark and 19th century pioneers who moved Americas borders westward. Just across the street from the Arch is another free attraction, the Old Courthouse. This historic building was the site of the famous Dred Scott slavery trial. Today, you can tour restored courtrooms and galleries.
The Museum of Westward Expansion is located under the Gateway Arch. It is open from 9 a.m. to 6 p.m. daily, with expanded summer hours from 8 a.m. to 10 p.m. The Old Courthouse is open daily from 8 a.m. to 4:30 p.m., except Thanksgiving, Christmas and New Years Day.
St. Louis has a ton of stuff to do. Missouri Botanical Gardens, the zoo, the arch, the Magic House... all great. We are headed to Gatlinburg for Spring Break. Haven't been since Summer of 2012, and I just need some pancakes from the Log Cabin Pancake House. 
