Pearelax is an After Effects script that lets you move 3d layers forward and backward in z space while maintaining their optical size and position. This lets you easily convert 2d illustrations into dynamic 3d scenes.
You move layers by a desired pixel amount or as a percentage of their current scale.
You can automatically stagger the amount across multiple layers in order to set up an entire scene with a single click.
For more precise controls, you can add an effect slider that uses expressions. Once you have your layer(s) positioned where you want, you can “bake” the expressions in order to clean up your project.