R.T.
The San Antonio Zoo is affordable and you can make a day of it by packing a picnic and enjoying the park and Zoo train. Also, the Riverwalk Extension is free and beautiful. Also, several museums, such as the Witte have free admission in the afternoon. Go to their websites for info. The Alamo and all other missions in town are free to visit with guided tours and tons of interesting stuff for kids to see, many are interactive as well, again, check their websites. Good luck and have a great Spring break!