In case you haven't heard and are interested in trying them out - Discovery Education streaming is FREE for the summer! Just sign up (FREE) with the homeschool buyers co-op and order your free trial.
It's a great deal for the summer and the homeschool buyers co-op has occasional sales for the program for $99 for the year. Well worth the price. They also have a program to build assignments, build quizzes, writing prompt builder and more. The quality of the video's is outstanding and engaging for k-12th grades.