The basic version of Sides costs $1.99 and contains the full text script for a specific play. For versions of Sides that have audio pre-recorded, you can either buy audio for specific acts within the program, or purchase a version that contains all the audio for $9.99.
There is also a free version that you can use to demo the features of the program.
No you don't! If you want to use the professional audio recorded by veteran actors, but only need a single act, you can do so by clicking on the "More" screen within the regular version of Sides, and selecting "Buy Professional Audio".
Please note, not every show has professional audio available! But if it does, you will see it there.